Process for the production of poly(3-hydroxyalkanoates)

ABSTRACT

Novel poly(3-hydroxyalkanoates), such as poly(3-hydroxybutyrate), and blends of these with other polymers are disclosed. A novel process for producing these poly(3-hydroxyalkanoates) is also disclosed which entails polymerizing one or more β-substituted-β-propiolactone(s) under polymerization conditions in the substantial absence of water in the presence of an anionic initiator.

This is a divisional application of application Ser. No. 08/185,097filed Jan. 21, 1994 now U.S. Pat. No. 5,391,708, which is a divisionalof Ser. No. 07/901,306 filed Jun. 19, 1992 now U.S. Pat. No. 5,281,691.

FIELD OF THE INVENTION

The present invention relates to novel poly(3-hydroxyalkanoates) andblends with other polymers. The present invention further relates to aprocess for the production of poly(3-hydroxyalkanoates) in thesubstantial absence of water in the presence of an anionic initiator.The present invention also relates to biodegradable articles producedfrom the poly(3-hydroxyalkanoates).

BACKGROUND OF THE INVENTION

Poly(3-hydroxyalkanoates) are naturally occurring thermoplasticpolymers-currently isolated from bacteria and other microorganisms.Unlike many thermoplastic polymers, poly(3-hydroxyalkanoates) and inparticular poly(3-hydroxybutyrate) have been shown to be biodegradableand environmentally non-persistent. Poly(3-hydroxyalkanoates) have theadditional feature of being both thermally and hydrolyticly unstable andthus can degrade without microbial intervention. However, the high costof processing and isolating poly(3-hydroxyalkanoates) derived fromnatural sources has inhibited the wide spread use of these biodegradablepolymers in commercial applications. A low cost synthetic method for thepreparation of poly(3-hydroxyalkanoates) is, therefore, highlydesirable.

Previous attempts at the production of poly(3-hydroxyalkanoates) by thepolymerization of β-substituted-β-propiolactones generally fall into twocategories, acid catalyzed reactions generally characterized by the useof Lewis acid catalysts containing metals such as aluminum or zinc, oranionic ring opening polymerizations. Examples of acid catalyzedpolymerization of β-substituted-β-propiolactones can be found in thework of Tani et al. (Macromolecules, 10, 275 (1977) and Lenz et al.(Macromolecules 21, 2657,(1988).

The Lewis acids most frequently used in the acid catalyzedpolymerizations have included triethyaluminium/water complexes (oftenreferred to as aluminoxanes) and diethyl zinc/water systems as well astransition metal alkoxides such as aluminum triisopropoxide.

Examples of anionic ring opening polymerization ofβ-substituted-β-propiolactones can be found in the work of Tani et al.(Macromolecules, 10, 275 (1977), Kricheldorf et al. (J. Macromol.Sci.-Chem. A26, 951 (1989), and the work of Jedlinski et al.Macromolecules, 24,349, 1991). These references generally disclose thatanionic ring opening polymerization occurs via nucleophilic attack atthe β-carbon of the β-substituted-β-propiolactones. However, this typeof polymerization is slow and produces low molecular weight polymers.Tani et al. also disclose that the anionic ring opening polymerizationof β-alkyl or β-haloalkyl-β-propiolactones using conventional anioniccatalysts either results in no ring opening or the termination ofpropagation at a very early stage.

Kricheldorf et al. disclose that, in solution or in bulk, non-ionicbases or ionic bases either result in no reaction or cause significantchain termination (often indicated by crotonate end group formation)during the ring opening polymerization of β-butyrolactone. Kricheldorfet al. isolated only low molecular weight polymer using reactiontemperatures of 50° C. and reaction times of 48 hours.

Jedlinski et al. using potassium naphthalide in terahydrofuran solutionin presence of 1S-crown-6 or cryptand [2, 2, 2] produced low molecularweight poly(3-hydroxybutyrate) from β-butyrolactone at room temperaturewith reaction times ranging from 96 to 200 hours. Using reaction timesof 80 to 100 hours, Jedlinski et al. also demonstrated the preparationof low molecular weight poly(3-hydroxybutyrate) from β-butyrolactoneusing potassium acetate/18-crown-6 or potassium crotonate/18-crown-6 asa polymerization initiator.

In light of the above it would be very desirable to be able to producepoly(3-hydroxyalkanoates) from β-substituted-β-propiolactones of highermolecular weights at increased reaction rates and higher yields.

SUMMARY OF THE INVENTION

The composition of the present invention comprises an atacticpoly(3-hydroxyalkanoate) containing stereorandom recurring units of theformula: ##STR1## wherein n is an integer from 700 to 12,000 and R andR¹ are each independently selected from saturated and unsaturated C₁ toC₂₀ alkyls, and subsitituted alkyls C₃ to C₁₀ aryls and substitutedaryls, and C₅ to C₁₀ cycloalkyls and substituted cycloalkyls and whereinR¹ can also be hydrogen.

A further composition of the present invention comprises apoly(3-hydroxyalkanoate) containing recurring units of the formula:##STR2## wherein n is an integer from 10 to 12,000; m is an integer ofat least 2; and R and R¹ are each independently selected from saturatedand unsaturated C₁ to C₂₀ alkyls and substituted alkyls, C₃ to C₁₀ arylsand substituted aryls, and C₅ to C₁₀ cycloalkyls and substitutedcycloalkyls, and wherein R¹ can also be hydrogen.

An additional composition the present invention comprises apoly(3-hydroxyalkanoate) containing recurring units of the formula:##STR3## wherein n is an integer from 10 to 12,000 and R and R¹ are eachindependently selected from saturated and unsaturated, C₁ to C₂₀ alkylsand substituted alkyls, C₃ to C₁₀ aryls and substituted aryls, and C₅ toC₁₀ cycloalkyls and substituted cycloalkyls.

An additional feature of the present invention comprises a blendcontaining i to 99% by weight of the above novelpoly(3-hydroxyalkanoates) and I to 99 weight % of at least one otherpolymer such as a polyether, a cellulose ester, a starch or starchester, a polyester, a polyesterether, or polyacrylate.

The process for producing poly(3-hydroxyalkanoates) according to thepresent invention comprises contacting a solution containing about I toabout 100 mole percent of at least one β-substituted-β-propiolactone,containing less than 5,000 ppm water, with an anionic initiator underpolymerization conditions to produce a poly(3-hydroxyalkanoate).

DETAILED DESCRIPTION OF THE INVENTION

Applicants have unexpectedly discovered high molecular weight atacticpoly(3-hydroxyalkanoates). Applicants have also unexpectedly discoverednovel poly(3-hydroxyalkanoates). The poly(3-hydroxyalkanoates) aregenerally prepared by a novel process for the anionic ring openingpolymerization of β-substituted-β-propiolactones (monomer) to producethe poly(3-hydroxyalkanoates). When using racemic monomer, this processtypically produces atactic polymer of low Tg which among other thingscan be used for blending with other polymers. Typically when usingchiral monomer or a mixture of chiral and racemic monomer, this processproduces isotactic or partially isotactic polymer with significantcrystalline regions.

As with other polymers, having similar physical properties, thepoly(3-hydroxyalkanoates) of the present invention are useful in manyapplications. These poly(3-hyroxyalkanoates) can be made into manydifferent articles either alone or as a blend with other compatiblepolymers such as molded articles, fibers, and films. Thesepoly(3-hydroxyalkanoates) can be formed into novel blends of, eitheratactic and/or isotactic polyhydroxyalkanoates, with cellulose esters,aliphatic polyesters, aromatic polyesters, starch and starch esters, andaliphatic/aromatic polyesters. Such blends withpoly(3-hydroxyalkanoates) have been found to be unexpectedlybiodegradable.

The composition of the present invention comprises the high molecularweight atactic poly(3-hydroxyalkanoate) containing stereorandomrecurring units of the formula: ##STR4## wherein n is an integer from700 to 12,000 and R and R¹ are each independently selected fromsaturated and unsaturated C₁ to C₂₀ alkyls and substituted alkyls, C₃ toC₁₀ aryls and substituted aryls, C₅ to C₁₀ cycloalkyls and substitutedcycloalkyls, and wherein R¹ can also be hydrogen and is preferablyhydrogen.

The term "alkyl" means straight or branched alkyl moieties of up to 20carbon atoms such as methyl, ethyl, n-propyl, isopropyl, n-butyl,isobutyl, sec-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl,docecyl, and the like. Preferred alkyl groups are C₁ to C₅ straight orbranched chain alkyls.

In the present invention, the substituted alkyls, aryls, and cycloakylspreferably have no more than 4 substituents with each substituent beingindependently selected from halo, C₃ -C₁₀ aryl, C₇ -C₁₂ arylakyl, C₁-C₁₀ alkoxy, C₁ -C₁₀ acyl, cyano, C₁ -C₁₀ carboxyalkyl, and C₂ -C₁₀acyloxy.

Examples of the above substituted alkyl groups include the cyanomethyl,nitromethyl, propionyloxymethyl, methoxymethyl, ethoxymethyl,1-butoxymethy, acetoxymethyl, chloromethyl, bromomethyl, iodomethyl,2,4-dichloro(n-butyl), 2-carbamoyloxyethyl and the like.

The term "C₁ to C₁₀ alkoxy" as used herein denotes groups of the formulaOR⁷ wherein R⁷ is hydrogen or alkyl. Examples of preferred C₁ to C₁₀alkoxy groups include methoxy, ethoxy, n-propoxy, isopropoxy, butoxy andlike groups.

The term "C₁ to C₁₀ acyl" or "acyl"-denotes groups of the formula##STR5## containing between 1 and 10 carbon atoms, wherein R⁶ ishydrogen, alkyl, aryl, substituted alkyl, arylalkyl, and substitutedarylalkyl.

Examples of preferred C₁ to C₁₀ acyl groups are those wherein R⁶ is a C₁to C₆ alkyl group such as methyl, ethyl, propyl, or butyl.

The term "C₂ to C₁₀ acyloxy" or "acyloxy" denotes of the formula##STR6## containing between 2 and 10 carbon atoms, wherein R⁶ is adefined here above with the exception that for acyloxy it is preferredthat R⁶ not be hydrogen. Examples of preferred C₁ to C₁₀ acyloxy groupsinclude those wherein R⁶ is a C₁ to C₆ alkyl group such as methyl,ethyl, propyl, or butyl. Further examples of preferred C₂ to C₁₀ acyloxygroups include those wherein R⁶ is a C₇ to C₁₂ arylalkyl group.

The term "C₁ -C₁₀ carboxyalkyl denotes groups of the formula ##STR7##wherein R⁶ is defined here above. Examples of preferred C₂ to C₁₀carboxyalkyl groups are those wherein R⁶ is a C₇ to C₁₂ alkyl group suchas methyl, ethyl, propyl, or butyl.

The term "halo" and "halogen" refer to the fluoro, chloro, bromo, oriodo groups.

The term "C₇ to C₁₂ arylalkyl" denotes a C₁ to C₆ alkyl groupsubstituted at any position by an aromatic ring. Examples of such agroup include phenylmethyl (benzyl), 2-phenylethyl, 3-phenyl-(n-propyl),4-phenyl-hexyl, 3-phenyl-hexyl, 3-phenyl-(n-amyl), 3-phenyl-(sec-butyl),and the like.

The term C₃ to C₁₀ aryl refers to any aromatic system includingheteroaromatic systems containing from 3 to 10 carbon atoms. Examples ofsuch systems include furyl, imidazolyl, pyridyl, phenyl, naphthyl, andthe like.

This high molecular weight polymer (I), is preferably essentiallylinear. In the high molecular weight atactic poly(3-hydroxyalkanoate) ofthe present invention (I), n is preferably an integer from 700 to10,000; preferably 700 to 5,000; with an integer of 2,000 to 5,000 beingmost preferred. The higher molecular weight atacticpoly(3-hydroxyalkanoate), (I), is generally useful in blends with otherpolymers.

The high molecular weight poly(3-hydroxyalkanoate), (I), preferably hasan inherent viscosity of 0.2 to 6 at 25° C. on a 0.5 g sample and 100 mlof a 60/40 by weight solution of phenol/tetrachloroethane, morepreferably 0.4 to 2. The higher inherent viscosities are generally morepreferred.

The high molecular weight atactic poly(3-hydroxyalkanoate), (I), of thepresent invention preferably has a polydispersity between 1 and 10, morepreferably between 1 and 3, even more preferably between 1 and 2, with apolydispersity between 1 and 1.7 being most preferred.

The high molecular weight atactic poly(3-hydroxyalkanoate) of thepresent invention can be a homopolymer containing identical recurringunits of the above formula or can be a copolymer in which R and R¹ ofthe recurring units are independently selected. Included within thecopolymers are the block copolymers in which the reoccurring units areidentical for only a portion of the entire polymer chain. R and R¹ arepreferably selected from C₁ to C₂₀ alkyls with the C₁ to C₅ alkyl beingmore preferred and with R¹ most preferably being hydrogen. The mostpreferred Poly(3-hydroxyalkanoate) is poly(3-hydroxybutyrate), meaning Ris methyl and R¹ is hydrogen.

Another composition of the present invention comprises 2 or morecovalently bound chains of poly(3-hydroxyalkanoate) containing units ofthe formula: ##STR8## wherein n is an integer from 10 to 12,000; m is aninteger of at least 2; and R and R¹ are each independently selected fromsaturated and unsaturated C₁ to C₂₀ alkyls and substituted alkyls, C₃ toC₁₀ aryls and substituted aryls, C₅ to C₁₀ cycloalkyls and substitutedcycloalkyls and R¹ can also be hydrogen.

In the formula, (II), above, P is preferably a monomeric carbon skeletonbackbone or polymeric skeleton backbone bearing polycarboxyfunctionality. An example of a polymeric skeleton backbone bearingpolycarboxyl functionality is a cellulose acetate succinate containingat least 2 or more carboxylate groups. Examples of monomeric carbonskeleton backbones are carboxy substituted alkyls such as1,2,3,-propanetricarboxylate and 1,2,3,4-butane tetracarboxylate.

In the formula (II), above, m is preferably an integer of 2 to 1,000.Alternatively m is preferably an integer of at least 3 with m being aninteger from 3 to 100 being most preferred.

In the composition of the present invention that contains chains ofpoly(3-hydroxyalkanoate) on P represented by formula (II), n can be aninteger from 10 to 12,000, but is preferably an integer from 150 to10,000. Process problems can result when m is a large integer and/orwhen n is a large integer, due to high viscosities when using minimalamounts of solvent. Additionally, higher reaction rates can be achievedwhen n is a smaller integer (150 to 1,000). Even in cases of small n,high molecular weight polymer can be obtained through the proper choiceof m.

As with the atactic poly(3-hydroxyalkanoate) of formula (I), the abovecomposition (II) containing the chains of poly(3-hydroxyalkanoate), ispreferably of higher molecular weight.

Preferably, poly(3-hydroxyalkanoate) of formula (II), has apolydispersity of greater than 1 up to 10, preferable greater than 1 upto 3, more preferable greater than 1 up to 2, with a polydispersity of1.05 to 1.7 being most preferred.

Such exceptionally narrow polydispersities result in a narrower range ofpolymer properties for any particular preparation. One very apparentadvantage of these narrow polydispersities is the nearly complete lackof low molecular weight components in polymers of high to mediummolecular weight.

Preferred R and R¹ in (II) are the same as the preferred R and R¹ in(I). As with high molecular weight atactic poly(3-hydroxyalkanoate) offormula (I), the branched poly(3-hydroxyalkanoate) of formula (II), canbe a homopolymer containing identical recurring units of the formula orcan be a copolymer, including block copolymer, in which R and R¹ of therecurring units are independently selected. The branchedpoly(3-hydroxyalkanoate) also preferably has an inherent viscosity of0.2 to 6 at 25° C. on a 0.5 g sample and 100 ml of a 60/40 by weightsolution of phenol/tetrachloroethane, more preferably between 0.4 to 2.Higher inherent viscosities are typically preferred. R and R¹ arepreferably selected from C₁ to C₅ alkyls with R¹ more preferably beinghydrogen, and R being methyl.

An additional composition of the present invention is the bisubstitutedpoly(3-hydroxyalkanoate) and comprises a poly(3-hydroxyalkanoate)containing recurring units of the formula: ##STR9## wherein n is aninteger from 10 to 12,000 and R and R¹ are each independently selectedfrom saturated and unsaturated C₁ to C₂₀ alkyls and substituted alkyls,C₃ to C₁₀ aryls and substituted aryls, and C₅ to C₁₀ cycloalkyls andsubstituted cycloalkyls. R and R¹ are preferably selected from C₁ to C₅alkyls.

In the poly(3-hydroxyalkanoate) composition with units of formula (III),n is preferably an integer from 150 to 10,000 more preferably 700 to10,000 and even more preferably 1,000 to 3,000.

As with the above high molecular weight atactic poly(3-hydroxyalkanoate)with units of formula (I), the bisubstituted poly(3-hydroxyalkanoate),(III), has a polydispersity of greater than 1 up to 10, preferablygreater than 1 up to 3, more preferable greater than 1 up to 2, with apolydispersity of 1.05 to 1.7 being most preferred. Thepoly(3-hydroxyalkanoate) also preferably has an inherent viscosity of0.2 to 6 at 25° C. on a 0.5 g sample and 100 ml of a 60/40 by weightsolution of phenol/tetrachloroethane, more preferably 0.4 to 2.

Novel poly(3-hydroxyalkanoates) are prepared in a novel processcomprising contacting a solution containing about 1 to 100 mole percentat least one β-substituted-β-propiolactone containing less than 5,000ppm water with an anionic initiator under polymerization conditions toproduce a poly(3-hydroxyalkanoate).

Applicants have unexpectedly discovered that prior methods of producinglow molecular weight poly(3-hydroxybutyrate) which is a specificpoly(3-hydroxyalkanoate) were not removing water to a significant extentfrom the monomer and thus were polymerizing the β-butyrolactone in highconcentrations of water. This relatively high concentration of water(above 5,000 ppm) is evidenced by the low production rates and lowmolecular weight material produced by prior art and the comparativeexamples that follow. Thus, prior to the present invention, the processof preparing β-substituted poly(3-hydroxyalkanoates) with monomercontaining less than 5,000 ppm water was nonexistent. Applicants haveunexpectedly discovered an improved process of producingpoly(3-hydroxyalkanoates) from a polymerization mixture that among otheraspects contains less than 5,000 ppm water. This improved processincreases production and molecular weight of thepoly(3-hydroxyalkanoates) due mostly to the lower water concentrationsduring polymerization. The applicants have been able to reduce theamount of water present during polymerization to well below 2000 ppm.The water concentration is preferably less than 1,000 ppm water, morepreferable less than 500 ppm with a concentration of water less than 250ppm being most preferred.

The process of the present invention unexpectedly produces thepoly(3-hydroxyalkanoates) at extremely high rates at high molecularweights and improved yields.

The β-substituted-β-propiolactones used in the present invention aremanufactured or processed to contain less then 5,000 ppm waterpreferably by distillation prior to use such that the generation ofβ-substituted-β-hydroxypropionate is minimized or that the decompositionof β-substituted-β-hydroxypropionate to produce water does not occur.

β-Substituted-β-propiolactones react with water or hydroxide to produceβ-hydroxycarboxylic acids. β-Hydroxycarboxylic acids and estersgenerally, in the presence of proper acid or base catalyst, can undergoelimination of water to produce α,β-unsaturated carboxylic acids oresters. The most frequently used and conventional method to purifyβ-substituted-β-propiolactones, and in particular β-butyrolactone,involves distillation from calcium hydride drying agents. The presentinventors have unexpectedly discovered the generation of water upondistillation of β-substituted-β-propiolactones, and in particularbutyrolactone, from calcium hydride. It is believed that the water isgenerated from β-hydroxycarboxylic acids or the salts derived therefromunder what was previously believed to be mild distillation conditions(for β-butyrolactone; 70° C., 20 mm Hg). The present inventors havefurther discovered that sufficient time or care needs to be taken duringthe distillative purification of β-substituted-β-propiolactone monomerin order to permit the generation and removal of low boilers (water).

Alternatively, a preferred method of reducing or removing the water inthe monomer liquid prior to polymerization can be accomplished by usinga selective distillation process. This distillation process entails acenter draw of high boilers for use in polymerization from thedistillation column with the simultaneous removal and, preferablyrecycle, of low boilers. This distillation process is preferablycontinuous.

It is also desirable that residual carboxylic acid content in themonomeric β-substituted-β-propiolactone be minimized. It is believedthat traces of carboxylic acids, if present during the polymerization,are capable of hydrogen bonding to the active carboxylate anionic sites(initiator and/or growing chains), thereby slowing the overall rate ofpolymerization. The number of carboxylic acid equivalents present in themonomer prior to initiation of polymerization is preferably less than0.5 mole %, more preferably less than 0.1 mole %, even more preferablyless than 0.01 mole % with less than 0.001 mole % being most preferred.

In a further process of the present invention the produced polymer,poly(3-hydroxyalkanoate), is precipitated to remove unreacted monomerinto the supernatant liquid. This precipitation is preferably conductedby dissolving the preferred poly(3-hydroxyalkanoate),poly(3-hydroxybutyrate) in acetic acid containing up to 60% water andthen the polymer is purified by precipitation into water. Higher amountsof acetic acid (70% or greater) are more preferred to enhance thesolubility of the polymer prior to precipitation. This precipitationadditionally serves to remove any catalyst/initiator from the polymer.Monomer can be further removed from the polymer by decomposition by theaddition of water or other suitable nucleophile to the polymer orpolymer solution preferably in the presence of an acid or base catalystand at elevated temperatures. The removal of monomer from polymer can beaccomplished by more than one decomposition or precipitation step. Afurther improvement in the process of removing unreacted monomer frompolymer entails, prior to precipitation into water, the heating of anaqueous acetic acid solution of poly(3-hydroxybutyrate) to decompose themonomer. This heating is at a temperature preferably between 60 and 140°C. and is preferably conducted for a time of at least one minute but notmore than 8 hours.

Blending of this polymer with another polymer can also be conductedprior to the aqueous precipitation process referred to herein above. Apreferred polymer that can be blended with the poly(3-hydroxyalkanoate)by precipitative blending is a cellulose ester of a DS 1.7 to 2.8.

In the process of the present invention theβ-substituted-β-propiolactones are of the formula: ##STR10## and theresulting polymer is of the formula: ##STR11## wherein n is an integerfrom 10 to 12,000 and R and R¹ are each independently selected from C₁to C₂₀ alkyls and substituted alkyls, C₃ to C₁₀ aryls and substitutedaryls, and C₅ to C₁₀ cycloalkyls and substituted cycloalkyls and whereinR¹ can also be hydrogen and is preferably hydrogen. As with formulas(I), (II), and (III), the substituted R and R¹ can have up to 4substituents with each substituent being independently selected fromhalo, C₃ -C₁₀ aryl, C₇ -C₁₂ arylakyl, C₁ -C₁₀ alkoxy, C₁ -C₁₀ acyl,cyano, C₁ -C₁₀ carboxyalkyl, and C₂ -C₁₀ acyloxy. It is most preferredthat (IV) be β-butyrolactone wherein R is methyl and R¹ is hydrogen. Insome cases, depending on the nature or substitution pattern of (IV), thestructural formula (V) overlaps or is included within the formulas (I),(II), and (III). However, it should be noted that structure (V) can beisotactic, syndiotactic, atactic or any combination thereof. Due to therelative ease of synthesis, it is preferred that (V) be isotactic,atactic or any combination thereof.

In one preferred embodiment of the present invention, the process ispreferably conducted with optically enrichedβ-substituted-β-propiolactone to produce at least partially isotacticpoly(3-hydroxyalkanoate) containing up to 95% R or S repeat units. Theβ-substituted-β-propiolactone is preferably at least partially enrichedsuch that one of the two possible enantiomers is present in anenantiomer excess of 30 to 100%, preferably 50 to 80%, with an opticalpurity of 30 to 70% being most preferred. The presence of small amountsof atactic regions are preferred in the isotacticpoly(3-hydroxyalkanoate). The presence of such atactic regions, whichresult from the use of partially optically enrichedβ-substituted-β-propiolactone, help to decrease the extent of thecrystalline regions and thus improve properties of the polymer. Thus apolymer containing up to 95% R or S repeat units is preferred.

The process of the present invention to producepoly(3-hydroxyalkanoates) is preferably conducted at a temperature ofabout 0° to 150° C., more preferably 25° to 90° C. with a temperature of25° to 60° C. being most preferred. At temperatures much below 0° C. thereaction rate, even in the substantial absence of water, is too slow tobe very practical whereas temperatures above 150° C. or even much above120° C. can result in polymer decomposition and uncontrollable reactionrates.

The process of the present invention is conducted in the presence of ananionic initiator preferably at a ratio of initiator toβ-substituted-β-propiolactone of 1/25 to 1/12,000 with a ratio of 1/200to 1/8,000 being more preferred and a ratio of 1/400 to 1/3000 beingmost preferred.

High amounts of initiators, such as ratios above 1/25 or above 1/200,result in lower molecular weight polymer which often results inundesirable polymer properties such as leaching of oligomer from thepolymer sample. Low amounts of initiator (such as 1/12,000) can resultin unduly long reaction times, exceptional sensitivity to initiatorpoison and inhibitors and potentially unacceptable high viscositybuildup during reaction. While high viscosities are generally desirablein the final polymer due to the correlation of viscosity with molecularweight, unduly high viscosities often make processing difficult.

Anionic initiators are preferably chosen from the group of carboxylateanions and the appropriate counterion (cation). Alternatively,non-carboxylate initiators can be used if they are capable of formingcarboxylate anions in situ.

Counterions can be chosen from the group of mono to pentavalent cations.Preferred cation (counterions) for the carboxylate initiators are thosecations which weakly coordinate to the carboxylate anion, thuspermitting the carboxylate anion to be more reactive. The cation of theanionic initiator is preferably selected from the alkaline earth metals,alkali metals, tetrasubstituted ammonium compounds, tetrasubstitutedphosphonium compounds, tetrasubstituted arsenic compoundstetrasubstituted antimonium compounds, tetrasubstituted bismuthiumcompounds, tertiary sulfonium compounds, and the transition metals. Forcations which contain substituents, such as tetrasubstituted ammoniumcompounds, the hydrogen substituent is undesirable. Also undesirable aresubstituents containing OH, amine N--H, SH, COOH and the like. Generallysubstituents containing groups which are capable of hydrogen bonding tothe carboxylate initiator or growing carboxylate chain are undesirable.It is preferred that the oxidation state of the metal cations be five orless, more preferably less than 3 and most preferably less than 2(monocations). Suitable examples include the carboxylate salts ofpotassium and cesium. The alkali metals are more preferably lithium,sodium, rubidium and cesium, even more preferably rubidium and cesiumwith cesium being most preferred. The most preferred metal carboxylateis a metal acetate such as cesium acetate. Another preferred cation forthe anionic initiator is a tetra-substituted ammonium or phosphoniumcation, more preferably a tetra-alkyl ammonium salt that is preferablytetra-alkyl ammonium carboxylate with tetrabutylammonium carboxylatebeing more preferred and tetrabutyammonium acetate being most preferred.

When the process of the present invention is directed toward thesynthesis of (II), the initiators will be formed from a salt of thepolyacid: ##STR12##

Additionally when the cation of the anionic initiator is chosen from thealkali metals or the alkaline earth metals, the anionic initiatorpreferably contains a chelating agent capable of complexing to thecation of the anionic initiator. The preferred chelating agent isselected from polyethers that are preferably present at concentrationsof at least 1 mole equivalent relative to the cation of the anionicinitiator. The preferred polyethers are crown ethers and cryptands.Suitable crown ethers and cryptands can be found in the book CrownEthers and Cryptands by George Gokel. Different crown ethers andcryptands will generally be preferred for different alkali metals andalkaline earth metals. Preferred crown ethers and cryptands include15-crown-5, 18-crown-6, [2.1.1]-cryptand, 12-crown-4, benzo-15-crown-5,cyclohexano-15-crown-5, benzo-18-crown-6,Z-syn-Z-dicylohexano-18-crown-6, E-anti-E-dicyclohexano-18-crown-6,E-syn-Z-dicylohexano-18-crown-6, dibenzo-18-crown-6, 21-crown-7,24-crown-8, [2.2.1]-cryptand, [2.2.2]-cryptand, and [3.2.2]-cryptand,with 18-crown-6 being most preferred. Thus a more preferred anionicinitiator/chelating agent system is a potassium carboxylate or cesiumcarboxylate in the presence of 18-crown-6. Some anionic initiators suchas the cesium carboxylate and tetraalkylammonium carboxylate functionvery well without the chelating agent. Even the potassium cation,present in potassium carboxylates like potassium acetate, is capable ofinitiating polymerization without the benefit of an added chelatingagent.

The conjugate acid of the anion of the anionic initiator preferably hasa pKa that is at or above 1.5. In the case where the conjugate acid is apolyacid, the last acid has a pKa over 1.5. The preferred pKa for theconjugate acid(s) of the anionic initiators(s) is preferably above 4.

The novel compositions of the present invention can be blended withanother compatible polymer. These blends comprise;

(a) 1 to 99 wt. % of at least one atactic poly(3-hydroxyalkanoate)containing stereorandom recurring units of the formula: ##STR13##wherein n is an integer from 50 to 10,000, more preferably n is aninteger between 700 and 3,000, and R and R¹ are each independentlyselected from C₁ to C₂₀ alkyls and substituted alkyls, C₃ to C₁₀ arylsand substituted aryls, and C₅ to C₁₀ cycloalkyls and substitutedcycloalkyls and R¹ can also be hydrogen;

(b) about 1 to 99 wt. % of at least one other polymer.

It is preferred that the polymer of (b) above be a compatible polymerthat forms a useful blend when combined with (a). It is preferred thatthese blends of (a) and (b) be miscible, partially miscible, or slightlymiscible.

It is preferred that the blends of the present invention be formulatedsuch that they are at least partially biodegradable. Blends of thepresent poly(3-hydroxyalkanoates) with isotacticpoly(3-hydroxyalkanoates) obtained from natural sources are alsocontemplated.

In one preferred embodiment, component (a) is comprised of at leastpartially isotactic poly(3-hydroxyalkanoate). This partially isotacticpoly(3-hydroxyalkanoate) preferably contains up to 95% R or S repeatunits.

As used herein in reference to polymers chosen from group b, the terms"alkyl" and "alkylene" refer to either straight or branched chainmoieties such as --CH₂ --CH₂ --CH₂ --CH₂ -- and --CH₂ CH(X)--CH₂ --.Also, all of the carbon atoms of the cycloalkyl and cycloalkylenemoieties are not necessarily in the ring structure, e.g., a C₈cycloalkyl group can be cyclooctyl or dimethylcyclohexyl. The term"oxyalkylene" refers to alkylene chains containing from 1 to 4 etheroxygen groups.

Suitable compatible polymers preferably include polyethers, celluloseesters, starch and starch esters, polyesters, polyesterethers,polyethers, and polyacrylates.

Preferred polyethers are selected from polyethylene oxide andpolypropylene oxide and polytetramethylene oxide. It is preferred thatthe polyethers have a molecular weight between 200 and 10,000. It ismore preferred that the polyethers have a molecular weight between 200and 4,000. Such polyethers are typically more readily available.

Preferred polyesters are selected from aliphatic polyesters, aromaticpolyesters, and aliphatic/aromatic polyesters. The aliphatic-aromaticcopolyesters are preferably comprised of repeat units of: ##STR14##wherein R² and R⁵ are selected from one or more of the following groupsconsisting of C₂ -C₁₂ alkylene or oxyalkylene; C₂ -C₁₂ alkylene oroxyalkylene substituted with one to four substituents independentlyselected from the group consisting of halo, C₆ -C₁₀ aryl, and C₁ -C₄alkoxy; C₅ -C₁₀ cycloalkylene substituted with one to four substituentsindependently selected from the group consisting of halo, C₆ -C₁₀ aryl,and C₁ -C₄ alkoxy; R³ is selected from one or more of the followinggroups consisting of up to C₁₂ alkylene; C₀ -C₁₂ oxyalkylene; C₀ -C₁₂alkylene or oxyalkylene substituted with one to four substituentsindependently selected from the group consisting of halo, C₆ -C₁₀ aryl,and C₁ -C₄ alkoxy; C₅ -C₁₀ cycloalkylene; and C₅ -C₁₀ cycloalkylenesubstituted with one to four substituents independently selected fromthe group consisting of halo, C₆ -C₁₀ aryl, and C₁ -C₄ alkoxy; R⁴ isselected from one or more of the following groups consisting of C₆ -C₁₀aryl, C₆ -C₁₀ aryl substituted with one to four substituentsindependently selected from the group consisting of halo, C₁ -C₄ alkyl,and C₁ -C₄ alkoxy. In a more preferred embodiment the aliphatic-aromaticcopolyester R² and R⁵ are independently selected from C₂ -C₆ alkylene,C₄ -C₈ oxyalkylene, and C₅ -C₁₀ cycloalkylene; R³ is selected from C₁-C₄ alkylene, C₂ -C₄ oxyalkylene, and C₅ -C₁₀ cycloalkylene; R⁴ isselected from C₆ -C₁₀ aryl.

Alternatively R² and R⁵ can be prepolymers selected from the groupconsisting of polyethyleneglycols, polypropyleneglycols, andpolytetramethyleneglycols. Suitable copolyesterethers and methods fortheir preparation are disclosed in U.S. Pat. No. 4,349,469 thedisclosure of which is incorporated herein by reference. Thepolyethyleneglycols, polypropyleneglycols, and polytetramethylenglycolspreferably have molecular weights between 200 and 2,000.

The above aliphatic-aromatic copolyesters can be prepared from anypolyester comprising a combination or combinations of dicarboxylic acidsor derivatives thereof, and diols. The dicarboxylic acids are preferablyselected from the group consisting of the following diacids: malonic,succinic, glutaric, adipic, pimelic, azelaic, sebacic, fumaric,2,2-dimethyl glutaric, suberic, 1,3-cyclopentanedicarboxylic,1,4-cyclohexanedicarboxylic, 1,3-cyclohexanedicarboxylic, diglycolic,itaconic, maleic, oxalic, 2,5-norbornanedicarboxylic, 1,4-terephthalic,1,3-terephthalic, 2,6-naphthalene dicarboxylic, 1,5-naphthalenedicarboxylic, and ester forming derivatives thereof, and combinationsthereof. The diols are preferably selected from the group consisting ofethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol,2,2-dimethyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,6-hexanediol,thiodiethanol, 1,3-cyclohexane-dimethanol, 1,4-cyclohexanedimethanol,2,2,4,4-tetramethyl-1,3-cyclobutanediol, triethylene glycol,tetraethylene glycol, di-, tri-, tetrapropylene glycol, and combinationsthereof.

Suitable preferred aliphatic-aromatic copolyesters are selected from thegroup consisting of poly(ethylene glutarate-co-terephthalate) at 15-70mole % terephthalate; poly(tetramethylene glutarate-co-terephthalate) at15-70 mole % terephthalate; poly(tetramethyleneglutarate-co-terephthalate-co-diglycolate) at 15-55 mole % terephthalateand 1-10 mole % diglycolate; poly(tetramethyleneadipate-co-terephthalate) at 15-70 mole % terephthalate; poly(ethyleneadipate-co-terephthalate) at 15-70 mole % terephthalate;poly(tetramethylene succinate-co-terephthalate) at 15-70 mole %terephthalate; poly(ethylene succinate-co-terephthalate)at 15-70 mole %terephthalate poly(ethylene glutarate-co-naphthalene dicarboxylate) at15-70 mole % naphthalene dicarboxylate; poly(tetramethyleneglutarate-co-naphthalene dicarboxylate) at 15-70 mole % naphthalenedicarboxylate; poly(tetramethylene adipate-co-naphthalene dicarboxylate)at 15-70 mole % naphthalene dicarboxylate; poly(ethyleneadipate-co-naphthalene dicarboxylate) at 15-70 mole % naphthalenedicarboxylate; poly(tetramethylene succinate-co-naphthalenedicarboxylate) at 15-70 mole % naphthalene dicarboxylate; poly(ethylenesuccinate-co-naphthalene dicarboxylate) at 15-70 mole % naphthalenedicarboxylate; and poly(ethylene glutarate-co-terephthalate) at 15-70mole % terephthalate.

The aliphatic-aromatic copolyesters preferably have 10 to 1000 repeatunits, with repeat units of 15 to 600 being more preferred.

In the aliphatic-aromatic copolyesters, the aromatic subunit containingR⁴ which is: ##STR15## is preferably 5 to 90 mole %, with an amount of15 to 70 mole % being more preferred.

The blend of the present invention preferably comprises 5 to 95 weightpercent poly(3-hydroxyalkanoate) and 5 to 95 weight percentaliphatic-aromatic copolyester. The blend of the present invention whenused in molded or extruded articles preferably contains 5 to 30 weightpercent poly(3-hydroxyalkanoate) and 70 to 95 weight percent aliphaticaromatic polyester. However, when used in film or fiber applications theblend preferably contains 15 to 50 weight percentpoly(3-hydroxyalkanoate) and 50 to 85 weight percent aliphatic-aromaticcopolyester.

The compatible aliphatic polyester used in the blends of the presentinvention is preferably selected from aliphatic polyester having repeatunits of the following structure: ##STR16## wherein R⁸ and R⁹ are eachindependently selected from C₂ -C₁₂ alkylene, or C₂ -C₁₂ oxyalkylene; C₂-C₁₂ alkylene or C₂ -C₁₂ oxyalkylene substituted with one to foursubstituents independently selected from the group consisting of halo,C₆ -C₁₀ aryl, and C₁ -C₄ alkoxy; C₅ -C₁₀ cycloalkylene; C₅ -C₁₀cycloalkylene substituted with one to four substituents independentlyselected from the group consisting of halo, C₆ -C₁₀ aryl, and C₁ -C₄alkoxy. R⁸ is preferably C₂ -C₆ alkyene, C₄ -C₈ oxyalkylene, or C₅ -C₁₀cycloalkylene more preferably C₂ -C₄ alkylene or C₄ -C₈ oxyalkylene; andR⁹ is preferably C₂ -C₁₀ alkylene, C₂ -C₄ oxyalkylene, or C₅ -C₁₀cycloakylene more preferably C₂ -C₄ alkylene. Alternatively R⁸ can beprepolymer selected from the group consisting of polyethyleneglycols,polypropyleneglycols, and polytetramethyleneglycols. Suitablecopolyesterethers and methods for their preparation are disclosed inU.S. Pat. No. 4,349,469. The polyethyleneglycols andpolytetramethylenglycols preferably have molecular weight between 200and 2,000.

The aliphatic copolyester used in the blends of the present inventionpreferably have 10 to 1,000 repeat units, with repeat units of 15 to 600being more preferred.

The above aliphatic polyesters can be prepared from a combination orcombination of dicarboxylic acids or derivatives thereof, and diols. Thedicarboxylic acids are preferably selected from the group of diacidsconsisting of malonic, succinic, glutaric, adipic, pimelic, azelaic,sebacic, fumaric, 2,2-dimethyl glutaric, suberic,1,3-cyclopentanedicarboxylic, 1,4-cyclohexanedicarboxylic,1,3-cyclohexanedicarboxylic, diglycolic, itaconic, maleic,2,5-norbornanedicarboxylic, ester forming derivatives thereof, andcombinations thereof; and the diols are preferably selected from thegroup of diols consisting of; the ethylene glycol, propylene glycol,1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,3-butanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,2,2,4-trimethyl-1,6-hexanediol, thiodiethanol,1,3-cyclohexanedimethanol, 1,4-cyclohexane-dimethanol,2,2,4,4-tetramethyl-1,3-cyclo-butanediol, diethylene glycol, triethyleneglycol, tetraethylene glycol, tetra-, tri-, dipropylene glycol andcombinations thereof.

The aliphatic polyester is more preferably selected from groupconsisting of poly(hexamethylene glutarate), poly(hexamethyleneadipate), poly(ethylene succinate), poly(butylene glutarate),poly(butylene adipate), poly(butylene succinate), poly(etylenegularate), poly(ethylene adipate), poly(diethylene glutarate),poly(diethylene adipate), poly(diethylene succinate) andpoly(hexamethylene succinate).

When the composition that is a blend of (a) and (b) contains analiphatic polyester as component (b) the components (a) and (b) arepreferably present in an amount of about 8 to about 40 wt % (a) andabout 60 to about 92 wt % (b); however, when the composition is used toform a molded or extruded object the amounts of components (a) and (b)are preferably present in the range of about 8 to about 20 wt % (a) andabout 80 to about 92 wt % (b); and when used to form a film or fiberpresent in the range of about 20 to about 40 wt % (a) and about 60 toabout 80 wt % (b).

The cellulose ester used in the blends of the present invention ispreferably a C₁ -C₁₀ ester of cellulose having a DS/AGU of about 1.7 to3.0 more preferably about 2.1 to 2.85; a Tg of about 85° to 210° C.,more preferably about 140° to 180° C.; and an inherent viscosity ofabout 0.2 to 3.0, more preferably about 0.5 to 1.5, deciliters/gram asmeasured at a temperature of 25° C. for a 0.5 g sample in 100 ml of a60/40 parts by weight solution of phenol/tetrachloroethane: Thiscellulose ester is preferably selected from the group consisting ofcellulose acetate, cellulose propionate, cellulose butyrate, celluloseacetate propionate, cellulose acetate butyrate, and cellulose propionatebutyrate, more preferably cellulose acetate propionate and celluloseacetate butyrate, with cellulose acetate propionate being mostpreferred.

A particularly preferred cellulose acetate propionate is one having aDS/AGU of about 2.50 to 2.75 in which the DS/AGU of acetyl ester is fromabout 4-30% of the total ester content.

When the composition that is a blend of (a) and (b) contains a celluloseester as component (b) the components (a) and (b) are preferably presentin an amount of about 5 to about 95 wt % (a) and about 5 to 95 wt % (b);more preferably 5 to 40 wt % (a) and 60 to 95 wt % (b), however, whenthe composition is used to form a film or fiber the amounts ofcomponents (a) and (b) are preferably present in the range of about 20to about 40 wt % (a) and about 60 to about 80 wt % (b).

Another group of compatible polymers useful in the blends of (a) and (b)have the follow structure: ##STR17## wherein R¹⁰ is selected from thegroup consisting of C₃ -C₅ alkylene or C₂ -C₁₂ alkylene substituted withone to four substituents independently selected from the groupconsisting of halo, C₆ -C₁₀ aryl, and C₁ -C₄ alkoxy. A more preferredpolymer within this group is polycaprolactone.

Another group of compatible polymers useful in the blends of (a) and (b)include polyvinyl acetate, partially hydrolyzed polyvinyl acetate, vinylacetate-ethylene copolymer, polyvinyl alcohol, polymethyl methacrylate,polyethyl methacrylate, polycarbonate, and hydroxypropyl cellulose.

The blends of components (a) and (b) can be formed into useful coatings,fibers, or shaped articles.

The films can be prepared such as by solvent casting, melt extrusion, orby a blown film process. Examples of uses for films include disposablepackaging material, agricultural mulch sheet, bed liners, the film partof a bandage, and diapers, such as the barrer film or outer cover of thediaper, diaper tabs or tape, or film base for diaper fasteners.

Examples of uses for coatings include coatings for controlled or slowrelease of substances into the environment such as use in the slowrelease of fertilizers.

Examples of shaped articles include eyeglass frames, toothbrush handles,tool handles, camera parts, razor parts, pen barrels, syringes, shampoobottles, toys, automotive trim, and packaging materials. A preferredclass of articles containing fiber are known as non-woven articles. Suchnon-woven articles are used in sanitary napkins, tampons, undergarmentliners, and diaper inner liners. The fibers of the blend of (a) and (b)can be prepared by spinning from a solvent or by thermal extrusion andcan be round or non-round such that the fiber retains a complexcross-sectional shape. Other uses of fibers include for example theconstruction of filter tow, fishing lines, fishnets, or surgicalclothing.

The blend composition can be prepared by many different methods thatadequately mix components (a) and (b). Suitable examples of mixinginclude the novel precipitative blends of the present invention as wellas casting from a solvent, and thermally compounding. The blends arepreferably formed by mixing components (a) and (b) in screw extruder ata temperature of 130°-185° C. with the poly(3-hydroxyalkanoate)preferably introduced into the extruder as a molten liquid.

EXAMPLES

The following examples are set forth to illustrate the present inventionbut are not intended to limit the reasonable scope thereof.

Proton and carbon nuclear magnetic resonance (NMR) spectra were recordedon a Varian Gemini 300 NMR instrument operating at 300 MHz in protonmode and 75 MHz in carbon mode. Spectra were plotted using Varianversion 6.3A software. Proton NMR spectra were typically run at aconcentration of 5 to 50 mg experimental compound per gram of solution.Carbon NMR spectra were typically run at a concentration of 50 mg pergram of solution.

Infrared spectra were recorded on a Nicolet 5DX Spectrophotometer andmajor peak minima are reported in reciprocal centimeters (cm ⁻¹). Thisinstrument is capable of typical resolutions of less than 4 reciprocalcentimeters. Infrared spectra were recorded from films (for oils) or KBrpellets for crystalline materials.

GPC data were acquired on a Waters Model 150C gel permeationchromatograph. The mobile phase was CHCl₃ or THF. The molecular weightsare reported in polystyrene equivalents.

Water analyses were accomplished by gas chromatography using a HP 5890instrument equipped with a 25 meter methyl silicon capillary column (J &W Scientific) using hydrogen carrier gas and thermal conductivitydetection. The precision of this method may be estimated based on theknown precision of this method for determination of water in THF. Thus,through the generation of a calibration curve with known standards inTHF, the standard deviation of this water analysis is estimated to be+/-10 ppm for a sample containing 100 ppm of water.

(R,S)-β-butyrolactone was purchased from Aldrich Chemical Company anddistilled from calcium hydride (20-30 mm Hg, bp ca. 70° C., argon bleedto adjust pressure). Distilled β-butyrolactone was stored in oven driedlaboratory glassware under an argon atmosphere. Prior to use of themonomer, the sealed glassware containing the distilled β-butyrolactonewas stored in a desiccator or polyethylene bag containing calciumsulfate as drying agent. Distilled β-butyrolactone was typically usedwithin several days of its distillation and was always used within amonth of its distillation date. After distillation, all transfers ofβ-butyrolactone were made into oven dried glassware using an oven driedcannula and a positive pressure of dry argon or nitrogen.

In polymerization reactions involving 18-crown-6, potassium acetate, ortetrabutylammonium acetate, analytical grade material was purchased fromAldrich and used without any further purification unless otherwisespecified. A stream of argon gas was, however, passed over any openglassware containing the above reagents during transfers involving thesematerials in order to minimize introduction of water into subsequentreactions.

In polymerizations of β-butyrolactone (BBL) the carboxylate saltfunctions both as an initiator (the carboxylate portion) and as acatalyst (the counterion and, when present, the counterion complexingagent). Thus as used herein, the terms initiator and/or catalyst areused to refer to the carboxylate salt (and when present the ioncomplexing agent) and are used interchangeably.

All polymerizations of β-butyrolactone were conducted at ambientpressure under a dry argon or nitrogen atmosphere.

EXAMPLE 1

(R,S)-Poly(3-hydroxybutyrate) made from freshly distilled(R,S)-β-butyrolactone, potassium acetate (KOAC), and 18-crown-6 (1/2000catalyst to monomer ratio):

A room temperature (ca. 24° C.), oven dried flask was chargedsequentially with β-butyrolactone (94.93 g, 1.10 moles), potassiumacetate (0.5386 g, 5.49 mmoles), and 18-crown-6 (1.56 g, 5.90 mmoles).Hereinafter this mixture is referred to as solution A. Solution A wasused within two hours of its preparation.

A second 300-ml oven dried flask was then charged with freshly distilledβ-butyrolactone (87.83 g, 1.02 moles) and then was equipped with an ovendried magnetic stirring bar and a thermometer. The water content of theβ-butyrolactone was not measured. This stirred reaction vessel was thencharged with a portion of solution A (10.32 g, containing 0.59 mmoles ofKOAc, final ratio of KOAC to BBL ca. 1/2000). There appeared at mostonly a slight exotherm (to ca. 26° C.) when the catalyst solution A wasadded. After six days of stirring, the solution was analyzed by NMR andno conversion of monomer could be detected. The magnetically stirredreaction solution was then heated to 60° C. After only one day ofheating at 60° C., ¹ H NMR showed about 13% conversion of monomer topolymer. After 27 days of heating at 60° C., no monomer could bedetected by ¹ H NMR (<1%) and heating of the reaction was discontinued.Roughly 2 mole % (relative to hydroxybutyrate subunits) of crotonate endgroups were however observed in the proton NMR. This is believed to bean indication of monomer and/or polymer breakdown during reaction. Theresulting polymer was not further treated or purified but was insteaddirectly solvent blended with cellulose acetate propionate (CAP 482-20obtained from Eastman Chemical Company, vide infra, Example 20).

GPC: (THF, uncorrected relative to polystyrene): Peak molecularweight=19,000

Mn=2700

Mw=9600

Polydispersity=3.5

EXAMPLE 2

(R,S)-Poly(3-hydroxybutyrate) made from freshly distilled(R,S)-β-butyrolactone, potassium acetate, and 18-crown-6(BBL/KOAc/18-crown-6=200/1/1.04):

A 300-ml oven dried flask was charged with freshly distilledβ-butyrolactone (101.69 g, 1.18 moles) and then was equipped with anoven dried magnetic stirring bar and a thermometer. The water content ofthe β-butyrolactone was not measured. Potassium acetate (0.58 g, 0.0059moles) and 18-crown-6 (1.63 g, 0.00617 moles) were then sequentiallyadded to the stirred reaction solution. Over a period of 10 minuteswithout external cooling (with stirring), the reaction temperature roseto 30° C. When the reaction temperature reached 37° C., a roomtemperature water bath was applied to the external surface of thereaction vessel and the reaction temperature returned to ca. 25° C. Mostbut not all of the potassium acetate dissolved prior to application ofthe cooling bath. In approximately 5 hours and 50 minutes (350 minutes)the solution was analyzed by proton NMR which indicated that 68%conversion of monomer to polymer had occurred. After a total of only oneday at room temperature, the conversion of monomer to polymer was 93%.In 28 days no monomer could be detected by NMR (<1%). Proton NMR alsogave no indication for the presence of crotonate end groups, indicatingminimal decomposition during the course of the reaction.

GPC (THF, uncorrected relative to polystyrene (PS): Peak MolecularWeight=20000

Mn=9930

Mw=14900

Polydispersity=1.5

Tg (DSC, second heating. 20 C./min)=0° C.

Inherent Viscosity (IV.)=0.26

¹ H NMR (CDCl₃, digital resolution=0.18Hz, line width of TMS at halfheight=0.71Hz): 5.32-5.16 (m, 1H), 3.69 (s, 18-crown-6, ca. 187/1calculated molar ratio of monomer units to 18-crown-6), 2.66-2.54 (m,1H), 2.47 (dd, J=15.6, 6.1, 0.5H), 2.46 (dd, J=15.5, 6.1, 0.5H), 2.02(s, acetate end group, ca. 146(+/-100)/1 of monomer units to acetate endgroups), 1.28 (d, J=6.1, 1.5H), 1.27 (d, J=6.1, 1.5H).

The detection of two doublets of doublets for the proton at 2.46, 2.47ppm (methylene proton, one of the protons on the carbon alpha to thecarbonyl) and of two doublets for the methyl group at 1.28, 1.27 ppm isassumed to be due to the detection of diad tacticity in the case of themethylene proton and due to incomplete resolution of triad tacticity inthe case of the methyl group. That the tacticity is totally random (i.e.atactic or stereorandom polymer) is indicated by the averaged ratio ofpeak heights for the two methyl groups (low field/high fieldresonances=0.997) and the averaged ratio of peak heights for the protonat 2.46, 2.47 ppm (low field/high field resonances=0.995).

The resulting polymer was then treated to remove potassium and18-crown-6. Thus, the crude polymer was dissolved in methylene chloride(1-2 L) and filtered through a scintered glass funnel to remove a smallamount of particulates (thought to be traces of undissolved potassiumacetate). The resulting stirred solution was treated with a high surfacearea sulfonic acid resin (H+ form, 14 g, Amberlyst XN-1010, Aldrich Cat.No. 21,640-2) for 3-4 hours at room temperature. The resulting solutionwas then slowly filtered through a 3.5 cm ID glass column containingmethylene chloride and (from bottom to top) Amberlyst XN-1010 (10.5 g,H+ form), Amberlyst XN-1010 (13.6 g, K+ form) and Amberlyst XN-1010(25.6 g, M+ form). The eluate was concentrated in vacuo (ca. 4 mm Hg,30° C., overnight) to provide an extremely viscous clear oil. Except forthe absence of the 18-crown-6 peak, the proton NMR was identical to thatpreviously obtained before resin treatment.

GPC (THF, uncorrected relative to Polystyrene (PS)) Peak MolecularWeight=21000

Mn=11600

Mw=15700

Polydispersity=1.4

Tg(DSC, second heating. 20° C./min)=-3° C.

IV.=0.26

Potassium analysis (atomic emission): 3 ppm

EXAMPLE 3

In a repetition of the above experiment in Example 2, careful attentionwas paid to obtain strictly anhydrous β-butyrolactone (BBL). Thus, froma 1,000 g distillation of β-butyrolactone from calcium hydride, only thelast 500 ml of distilled material was collected. GC analysis suggested288 ppm of water in the lastly distilled β-butyrolactone. Usingβ-butyrolactone distilled in this fashion, 82% conversion of monomer(proton NMR analysis) was achieved in 5 hours and 40 minutes using theabove conditions (30°-33° C., BBL/KOAc/18-crown-6=193/1/1.01).

Caution needs to be taken when polymerizing this very dry BBL. We haverecently discovered that when extra care is taken to rigorously removemoisture from distilled β-butyrolactone (i.e. by discarding the firsthalf of the distillate from calcium hydride), vigorous exotherms oftenresult following the addition of our superior catalyst systems to neatBBL, even when using room temperature water (cooling) baths. Thesevigorous exotherms (up to 100° C. for a 100 g solution using a >1000 gwater bath) have been observed up to six hours following the addition ofcatalyst (potassium acetate/18-crown-6 or tetrabutylammoniumcarboxylates).

EXAMPLE 4

(R,S)-Polyhydroxybutyrate made from freshly distilled(R,S)-β-butyrolactone and tetrabutylammonium acetate (1/580 catalystratio):

A 300-ml oven dried flask was charged with freshly distilledβ-butyrolactone (110.93 g, 1.29 moles) and then was equipped with anoven dried magnetic stirring bar and a thermometer. The water content ofthe β-butyrolactone was not measured. Tetrabutylammonium acetate (0.67g, 0.00222 moles) was then added. There appeared at most only a slightexotherm (ca. 1.5° C./minute) when the catalyst was added. A watercooling bath was used when the reaction temperature reached 26° C. Inapproximately 6 hours and 40 minutes (400 minutes), the solution wasanalyzed by proton NMR which indicated that 42% conversion of monomer topolymer had occurred. After a total of only one day of reaction, theconversion of monomer to polymer was 84%. After a total of 71 daysfollowing initiation of the reaction, no monomer could be detected byNMR (<1%). Proton NMR gave no indication for the presence of crotonateend groups, indicating minimal decomposition during the course of thereaction.

GPC (THF, uncorrected relative to Polystyrene (PS): Peak MolecularWeight=38,000

Mn=23,700

Mw=31,000

Polydispersity=1.3

GPC (CHCl₃, uncorrected relative to Polystyrene (PS): Peak MolecularWeight=42,000

Mn=36,100

Mw=42,700

Polydispersity=1.2

Tg (DSC, second heating. 20 C/min) 4.5

IV.=0.427

¹ H NMR (CDCl₃, digital resolution 0.184 Hz, line width of TMS at halfheight=0.60 Hz): 5.32-5.16 (m, 1H), 2.66-2.54 (m, 1H), 2.47 (dd, J=15.4,6.1, 0.5H), 2.46 (dd, J=15.7, 6.1, 0.5H), 2.02 (s, acetate end group,insufficient signal to permit an accurate integral), 1.28 (d, J=6.1,1.5H), 1.27 (d, J=6.1, 1.5H) (The proton NMR of PHB produced fromtetrabutylammonium acetate is judged to be superimpossable with theproton NMR obtained for PHB prepared from KOAc/18-crown-6. The tabulatedproton NMR is duplicated here to permit a direct comparison withpotassium acetate/18-crown-6 prepared material). That the tacticity istotally random (i.e. atactic or stereorandom polymer) is indicated bythe averaged ratio of peak heights for the two methyl groups (lowfield/high field resonances 1.002) and the averaged ratio of peakheights for the proton at 2.46, 2.47 ppm (low field/high fieldresonances 1.004).

EXAMPLE 5

In a repetition of the above experiment of Example 4, careful attentionwas paid to obtain strictly anhydrous β-butyrolactone (BBL). Thus, froma 1,000 g distillation of β-butyrolactone from calcium hydride, only thelast 500 ml of distilled material was collected. GC analysis suggested288 ppm of water in the lastly distilled β-butyrolactone. Usingβ-butyrolactone distilled in this fashion, 69% conversion of monomer(proton NMR analysis) was achieved in six hours and 10 minutes using theabove conditions (29°-33° C. BBL/tetrabutylammonium acetate=586/1).

EXAMPLE 6

(R,S)-poly(3-hydroxybutyrate) made from freshly distilled(R,S)-β-butyrolactone and tetrabutylammonium acetate 1/2450 catalystratio):

The β-butyrolactone used in this reaction was obtained as a lastdistillate cut (500 ml) from a ca. 1.25 liter distillation from calciumhydride. Water analysis (gc) revealed 447 ppm of water in theβ-butyrolactone used in this reaction.

A 300-ml oven dried flask equipped with an oil filled thermowell wascharged with β-butyrolactone (153.6, 1.78 moles) and then was equippedwith an oven dried mechanical stirrer. Tetrabutylammonium acetate (0.219g, 0.000728 moles) was then added. Over a period of approximately 1 hourthe reaction temperature rose to 29° C. (as monitored via a thermocouplein the reactor thermowell). After a total of 395 minutes (reaction stillat 29° C. without external cooling or heating), proton NMR analysisindicated the conversion of 40% of the monomer into polymer. The nowviscous reaction mixture was left to stir overnight. Overnight thereaction temperature returned to room temperature (23°-24° C.). After atotal of 23 hours and 15 minutes, proton NMR analysis indicated 51%conversion of monomer into polymer. Stirring was then ceased. After atotal of 37 days, proton NMR analysis indicated 88% conversion ofmonomer to polymer.

GPC (THF, uncorrected relative to Polystyrene (PS): Peak MolecularWeight=149,000

Mn=84,000

MW=111,000

Polydispersity=1.32

Acetic acid (100 ml) was added to the very viscous polymer sample andtwo layers resulted. The reaction vessel was placed in a 60° C. sandbath and heated for 3 hours with periodic manual stirring with a spatulaat the interface of the two layers. An additional portion of acetic acidwas added (25 ml) and the reaction mixture was allowed to cool to roomtemperature overnight. The top acetic acid layer was decanted and anadditional portion (125 ml) of acetic acid was added to the top of thepolymer layer. Heating was continued throughout the day with occasionalmanual stirring between the two phases. The reaction mixture was onceagain left to cool to room temperature overnight. The top acetic acidlayer was decanted and an additional portion (125 ml) of acetic acid wasadded to the top of the polymer layer. The reaction vessel was onceagain heated in a 60° C. sand bath and after approximately 4 hoursmechanical stirring was initiated. After a total of 8 hours (for thisthird acetic acid wash) heating was terminated and the polymersolution/mixture was left to stir overnight. After stirring overnightall of the polymer has dissolved. All acetic acid solutions werecombined and charged into a dropping funnel. Additional acetic acid (25ml) was added to bring the total volume of added acetic acid to 400 ml.This acetic acid solution of polymer was then added dropwise to amechanically stirred solution of water (1600 ml) at room temperature.After the addition of polymer solution was complete, there resulted aviscous polymer phase under the water/acetic acid solution. Proton NMRanalysis (DMSO-d6) of the polymer sample revealed the presence ofapproximately 2% by weight of β-butyrolactone. The polymer sample wasdissolved in 700 ml of acetic acid at room temperature and precipitatedas above from 2800 ml of distilled water. This precipitation wasrepeated a final third time (700 ml acetic acid, 2800 ml H₂ O). ProtonNMR revealed the complete absence of signals for β-butyrolactone. Theresulting polymer sample was dissolved in methylene chloride (1200 ml)and a small amount of remaining water was removed by use of a separatoryfunnel. The methylene chloride phase was washed with water (2×300 ml)and filtered through sodium sulfate. The resulting polymer wasconcentrated in vacuo (ca. 100 mm Hg and then 1-4 mm Hg) for severaldays. The resulting polymer was redissolved in methylene chloride (asmall amount of acetic acid was detected by proton NMR) and washed withadditional portions of water 3×200 ml). The resulting solution wasconcentrated in vacuo for 3 days. There resulted a clear viscous polymersample (100.96 g, 66%) which was shown to contain less than 3 weightpercent of methylene chloride by proton NMR. The proton NMR wasidentical with that obtained for the polymer in Example 4, although thesinglet attributed to the methyl group of the acetate end group wasnoticeably smaller in this sample.

GPC (THF, uncorrected relative to Polystyrene (PS): Peak MolecularWeight=78,000

Mn=47,000

Mw=75,000

Polydispersity=1.59

Tg (DSC, second heating 20/C./min)=0.4° C.

Inherent Viscosity: 0.785

Nitrogen Analysis (Dohrmann): 1 ppm

(Theory for no catalyst removal=66 ppm)

EXAMPLE 7

(R,S)-Poly(3-hydroxybutyrate) made from freshly distilled(R,S)-β-butyrolactone and tetrabutylammonium salt of1,2,3-propane-tricarboxylate (1/2000 catalyst to monomer ratio,expressed on a molar basis, 1/670 catalyst to monomer ratio expressed onan equivalent basis):

Catalyst Preparation: 1,2,3-Propane-tricarboxylic acid (tricarballylicacid, 75.9 g, obtained from Aldrich) was purified by recrystallizationfrom hot ethyl acetate (750 ml) and isopropanol (200 ml). The resultingsolution was allowed to cool to near room temperature and was thenfiltered away from a brown solid which had precipitated. The resultingfiltrate was then concentrated in vacuo to approximately 1/4 volume withsome resulting solids formation. This suspension was then brought toreflux which caused most but not all of the solids to go into solution.The resulting suspension was then allowed to cool to room temperatureand was left to stand overnight. The thus formed crystals were isolatedby filtration, washed with ethyl acetate and air dried (49.8 g).

A 40 wt % aqueous solution of tetrabutylammonium hydroxide (108.8 g,0.168 moles) was added with stirring to the recrystallized1,2,3-propane-tricarboxylic acid (10.09 g, 0.0573 moles, 0.172 normalacid equivalents). The resulting solution was allowed to stir overnightprior to filtration to remove a small amount of undissolved solids. Thefiltrate was frozen, placed on a lyophilizer and brought to constantweight (42.50 g). There was thereby obtained a white hygroscopic solidwhich was not purified further before using as a catalyst/initiator inthe polymerization of β-butyrolactone. All subsequent manipulations ofthis catalyst were carried out under a dry argon atmosphere.

A 300-ml oven dried flask was charged with freshly distilledβ-butyrolactone (114.03 g, 1.3245 moles) and then was equipped with anoven dried mechanical stirrer and a thermometer. The water content ofthe β-butyrolactone was not measured. The tetrabutylammonium salt of1,2,3-propane-tricarboxylic acid (0.59 g, 0.000655 moles) was then addedwith stirring to the reaction vessel. The resulting solution turnedslightly cloudy and there appeared to be no sign of any exotherm. Thetemperature of reaction never exceeded 32° C. After 18 hours and 20minutes the solution was analyzed by NMR and the conversion of monomerto polymer was 38%. In (49 hours and 50 minutes) the conversion ofmonomer to polymer was 67%. Stirring of the reaction was stopped after50 hours due to the high viscosity of the thus formed polymer. After 15days the conversion of monomer to polymer was 93%.

After six months at room temperature, NMR analysis revealed the completedisappearance of monomer. GPC analysis revealed the presence of 2 peaks.One high molecular weight peak of very narrow polydispersity and onesomewhat lower molecular weight peak of broader polydispersity.

IV=0.63

1st Peak (GPC, THF) Peak Molecular Weight=104,000

Mn=104,000

Mw=109,000

Polydispersity=1.05

2nd Peak (GPC, THF) Peak Molecular Weight=50,000

Mn=23,000

Mw=36,000

Polydispersity=1.6

EXAMPLE 8

(R,S)-Polyhydroxybutyrate made from freshly distilled(R,S)-β-butyrolactone and tetrabutylammonium salt of1,2,3,4-butane-tetracarboxylate (1/2400 catalyst ratio):

Catalyst preparation: An aqueous solution containing 40 wt % oftetrabutylammonium hydroxide was added with stirring to 1,2,3,4butane-tetracarboxylic acid (Aldrich). The resulting solution wasallowed to stir overnight. This homogeneous solution was then frozen,placed on a lyophilizer and brought to constant weight. There wasthereby obtained a white hygroscopic solid which was not purifiedfurther before using as a catalyst/initiator in the polymerization ofβ-butyrolactone. The water content of this catalyst was not measured.All subsequent manipulations of this catalyst were carried out under adry argon atmosphere.

A 300-ml oven dried flask was charged with freshly distilledβ-butyrolactone (155.30 g, 1.8039 moles) and then was equipped with anoven dried mechanical stirrer and a thermometer. A water content of 288ppm in this β-butyrolactone was suggested by gc analysis. Thetetrabutylammonium salt of 1,2,3,4-butane-tetracarboxylate (0.87 g,0.0007474 moles) was then added with stirring to the reaction mixture.To avoid the possibility of an uncontrolled exotherm, an air pistondriven jack containing a 0° C. cooling bath was utilized to cool thereaction when the reaction temperature reached 32.5° C. As the reactiontemperature then dropped, the jack was then removed from the vicinity ofthe reaction vessel to prevent excessive cooling. Thus, the temperatureof the reaction was held at a constant temperature of ca. 30°-33° C.throughout the day. In approximately 5 hours (300 minutes) the solutionwas analyzed by proton NMR and the conversion of monomer to polymer wasdetermined to be 57%. Stirring of the reaction mixture was discontinuedapproximately 6 hours after the addition of catalyst/initiator. After atotal of 17 days, NMR analysis indicated only 1% of monomer remained.

After six months at room temperature, NMR analysis revealed the completedisappearance of monomer. GPC analysis revealed the presence of 2 peaks,one high molecular weight peak of very narrow polydispersity and onesomewhat lower molecular weight peak of broader polydispersity.

IV.=0.701

1st Peak (GPC, THF) Peak Molecular Weight=139,000

Mn=128,000

Mw=137,000

Polydispersity=1.07

2nd Peak (GPC, THF)

Peak Molecular Weight=46,000

M (n)=25,000

M(w)=36,000

Polydispersity=1.45

EXAMPLE 9

(S)-Poly(3-hydroxybutyrate) made from freshly distilled(S)-β-butyrolactone and tetrabutylammonium acetate (299/1):

(S)-β-butyrolactone was prepared according to the method of Seebach (R.Breitschuh, D. Seebach, Chimia. 44,216 (1991).

A 25-ml oven dried flask was charged with freshly distilled(S)-β-butyrolactone (5 ml, 5.28 g, 0.0613 moles) and then was equippedwith an oven dried magnetic stirring bar and a thermometer. The watercontent of the (S)-β-butyrolactone was not measured. Tetrabutylammoniumacetate (0.02930 g, 0.0000972 moles) was then added. There appeared tobe no sign of any exotherm when the catalyst was added. After one day atroom temperature, the reaction solution was analyzed by NMR and therewas no detection of polymer. More tetrabutylammonium acetate (0.0325 g,0.0001078 moles) was then added. After six days there was still nodetection of polymer in the reaction. The reaction was left stirringover the weekend and when next examined (after a total of 13 days) thereaction mixture had solidified into white solids. Stirring of thereaction mixture ceased sometime between 6 and 13 days. After a total of13 days of reaction, proton NMR analysis of the reaction mixtureindicated that 28% conversion of the monomer to a crystalline polymerhad occurred. The proton NMR of this polymer was superimposible on theproton of NMR of natural polymer obtained from biological sources(Aldrich).

EXAMPLE 10

(R,S)-Poly(3-hydroxybutyrate) made from freshly distilled(R,S)-β-butyrolactone and cesium acetate (1/195 catalyst ratio):

β-Butyrolactone (111.31 g, 1.29 moles) and cesium acetate (1.27 g,0.00662 moles) were charged to a room temperature 300 ml oven driedflask which was equipped with a thermometer and a magnetic stirring bar.The water content of the β-butyrolactone was not measured. The reactionmixture was then heated at 60° C. over the weekend. After three days ofreaction at 60° C., proton NMR analysis indicated 85% conversion ofmonomer to polymer.

EXAMPLE 11

This example demonstrates the unexpected generation of water during thedistillation of β-butyrolactone.

A two liter, 1-neck flask was charged with β-butyrolactone (1 kg,Aldrich Lot #05627PD) and calcium hydride (14.07 g, -1 to 4 mesh) underan argon atmosphere. The resulting suspension was left to stirovernight. The following morning a 1 ft. vigreux column and a vacuumcompatible distillation take-off head was attached to the two literflask containing the β-butyrolactone and calcium hydride. The internalpressure in the distillation flask was brought to 25 mm Hg using avacuum pump with an argon bleed which permitted upward adjustment of thepressure. The distillation flask was vigorously stirred with heating anddistillation commenced at a head temperature of 70° C. Afterdistillation of the first approximately 40 ml of β-butyrolactone (F1),the first collection vessel was replaced to allow collection of a secondfraction (F2). There resulted shortly thereafter the observation that asecond liquid was condensing around the top ring of the water cooledcondenser while the major liquid (presumed to be β-butyrolactone)continued to condense around the bottom ring of the condenser. Thissecond presumably lower boiling liquid was observed to be sparinglysoluble in the higher boiling component (β-butyrolactone). Both liquidswere drawn off into the distillation receiver. Simultaneous with thegeneration of this apparent lower boiling component there was observed avigorous frothing of the components in the half-filled distillationvessel. The internal pressure in the distillation apparatus was observedto rise to approximately 40 mm Hg after which the pressure slowlydeclined over a period of several minutes back to the 25 mm set point.This temporary rise in pressure served to moderate the vigorous frothingwhich was observed in the distillation vessel. After approximately 5minutes all evidence for the generation of a second lower boilingcomponent had ceased and the two liquids phases which had been initiallyobserved in the distillation receiver had become homogeneous.Distillation was continued until approximately 250 ml of liquid had beencollected (F2). A final 500 ml of distillate was then collected (F3).

Gas chromatographic analysis (GC) of all distillate fractions revealedthat the major component was β-butyrolactone. GC analysis of thedistillate fractions for water revealed the following results.

F1: (40 ml) 551 ppm H₂ O

F2: (250 ml) 1347 ppm H₂ O

F3: (500 ml) 310 ppm H₂ O

The above procedure was repeated using 21.26 g of calcium hydride andprovided the following results:

F1: (30 ml) not analyzed for water

F2: (200 ml) 4881.ppm H₂ O

F3: (500 ml) 288 ppm H₂ O

EXAMPLE 12

This example demonstrates the effect of heating and water content on thedecomposition of β-butyrolactone in acetic acid.

A 50 ml volume of the indicated acetic acid/water solvent system wasbrought to the indicated temperature (generally reflux). A 5 ml sampleof β-butyrolactone was then added in one portion. The resulting stirredsolution was then heated for the indicated time prior to proton NMRanalysis for the reaction products. The results are presented in Table1.

                  TABLE 1                                                         ______________________________________                                        Decomposition of β-Butyrolactone                                         % Water in                                                                    HOAc      Time (min)  Temp (C.) % Decomp                                      ______________________________________                                         0        40          118       25                                            10        40          110       60                                            30        40          105       90                                            10        300         110       100                                           10        300          25        0                                            ______________________________________                                    

EXAMPLE 13

This example demonstrates the removal of β-butyrolactone from atacticpolyhydroxybutyrate by precipitation of the polymer into water.

A partially polymerized sample of (R,S)-β-butyrolactone was analyzed byproton NMR and was found to contain 62% β-butyrolactone (38%poly(3-hydroxybutyrate)). A 10 ml volume of this partially polymerizedsample was added by dropwise addition to a solution containing 20%acetic acid in water (v/v, 90 ml). The resulting precipitate was thendissolved in acetic acid (10 ml) and added by dropwise addition to asolution containing 10% acetic acid in water (90 ml). The resultingprecipitate was again dissolved in acetic acid (10 ml) and precipitatedby dropwise addition to a stirred solution containing 10% acetic acid inwater (90 ml). Each precipitate was analyzed for β-butyrolactone contentby proton NMR (DMSO-d₆) and the results are presented in Table 2.

                  TABLE 2                                                         ______________________________________                                        Precipitation of PHB                                                          Number of                                                                     PPT from Aqueous HOAc                                                         (80% Water)        % BBL                                                      ______________________________________                                        0                  62                                                         1                  13                                                         2                  <1                                                         3                   0                                                         ______________________________________                                    

The above three precipitations were repeated without analysis of any ofthe intermediate precipitates in order to maximize yield. Thus, from aninitial 11.03 g of poly(3-hydroxybutyrate) in β-butyrolactone (62%),there was obtained after 3 precipitations into acetic acid/water (20/80)a purified polymer sample. No residual monomer could be detected in thefinal precipitate. This final precipitate was dissolved in methylenechloride and filtered through sodium sulfate. The resulting solution wasconcentrated in vacuo (1-4 mm Hg) for several days to provide thecolorless polymer sample (3.68 g, ca. 88% recovery based on the initialNMR analysis). The proton NMR spectra of this sample were identical withthose obtained for Example 4 and indicated the presence of less than 2weight percent of methylene chloride.

GPC (THF, uncorrected relative to Polystyrene (PS) Peak MolecularWeight=21,000

Mn=16,000

Mw=19,000

Polydispersity=1.18

EXAMPLE 14

This example demonstrates the ability to recover poly(3-hydroxybutyrate)without significant decomposition (molecular weight change) whiletreating the crude polymer under conditions which decompose monomer.

A solution of 70% acetic acid in water (100 ml) was brought to refluxthrough the use of heating mantle applied externally to the reactionvessel (300 ml/3-neck flask). To this vigorously stirred solution wasadded the polymer sample (10 ml) containing 62% of β-butyrolactonemonomer which had been used in the Example 13. Reflux was maintained for30 minutes at a pot temperature of 104° C. after the addition ofpolymer. The heating mantle was then removed from the reaction vessel,thus permitting the reaction mixture to rapidly return to roomtemperature.

The above cooled reaction solution was placed in a dropping funnel andprecipitated by dropwise addition into a magnetically stirred solutionof distilled water (350 ml). The resulting precipitate was shown tocontain less than 2% of β-butyrolactone by proton NMR analysis.

GPC (THF, uncorrected relative to Polystyrene (PS) Peak MolecularWeight=20,000

Mn=11,000

Nw=14,000

Polydispersity=1.30

EXAMPLE 15

This example demonstrates the detrimental effect of water on thepolymerization rate of β-butyrolactone.

The β-butyrolactone used in these reactions was obtained as a lastdistillate cut (500 ml) from a one liter distillation from calciumhydride (70° C., 30 mm Mg). Water analysis revealed 176 ppm of water inthis distilled d-butyrolactone.

A 300 ml oven dried flask equipped with an oil filled thermowell wascharged with β-butyrolactone (144.25 g, 1.6756 moles) and then wasequipped with an oven dried mechanical stirrer. Tetrabutylammoniumacetate (0.86 g, 0.00285 moles) was then added with stirring at roomtemperature. The reaction was allowed to warm to 32° C. (ca. 10-20minutes) The reaction temperature was then maintained between 29 and 33°C. using a temperature actuated cooling bath (0° C.). After a total of195 minutes, a drop of the reaction mixture was diluted with 1 ml ofchloroform and immediately analyzed by proton NMR for percent conversionof monomer (reported conversion taken as the average of the polymer andmonomer methine, methylene, and methyl area ratios).

The above procedure was then repeated on two sequential days with thesame sample of distilled β-butyrolactone but with the addition of smallamounts of water to the β-butyrolactone prior to catalyst addition. Theresults are presented in Table 3.

                  TABLE 3                                                         ______________________________________                                        Detrimental Effect of Added Water to Polymerization Rate                      Catalyst/                                                                             Water    Reaction             Time                                    Monomer (ppm)    Temp. °C.                                                                         % Conversion                                                                            (min)                                   ______________________________________                                        1/587   176*     29-33      81        195                                     1/578   856**    29-32      48        197                                     1/552   2790***  21-25****   8        200                                                                 14        380                                                                 43        1335                                    ______________________________________                                         *Water content determined by gc analysis                                      **Prepared by addition of 100 μl of water to 146.98 g of butyrolactone     containing 176 ppm of water.                                                  ***Prepared by addition of 400 μl of water to 152.65 g of butyrolacton     containing 176 ppm of water.                                                  ****The upper limit for the temperature of these reactions was controlled     using a temperature actuated cooling (0° C.) bath. This reaction       was not sufficiently exothermic to actuate the bath.                     

EXAMPLE 16

A number of additional experiments were conducted according to thegeneral procedure described in Example 15. These experiments demonstratethe ability of different initiators and different initiatorconcentrations to successfully induce polymerization of β-butyrolactoneat low water concentrations. The results are summarized in Table 4. Someof the previously described examples are also presented in this Tablefor comparison.

                                      TABLE 4                                     __________________________________________________________________________    Catalyst/                                                                            Initiator/*                                                                         GC Water Content                                                                             % Conversion                                                                          Calc.**                                   Initiator                                                                            Monomer                                                                             In Water  Time NMR     MWT.                                      __________________________________________________________________________    a (Ex. 8)                                                                            1/2400                                                                              288 ppm   300 min                                                                            57      210,000                                   b (Ex. 3)                                                                            1/193 288 ppm   340 min                                                                            82      17,000                                    c (Ex. 5)                                                                            1/586 288 ppm   370 min                                                                            69      50,000                                    c      1/590 447 ppm   219 min                                                                            84      51,000                                    c (Table 3)                                                                          1/587 176 ppm   195 min                                                                            81      50,000                                    c      1/1292                                                                              447 ppm   405 min                                                                            68      100,000                                   c*** (Ex. 6)                                                                         1/2450                                                                              447 ppm   395 min.                                                                           40      211,000                                   d      1/1050                                                                              288 ppm   300 min                                                                             6      90,000                                    __________________________________________________________________________     a = tetrabutylammonium tetrasalt of 1,2,3,4butane-tetracarboxylic acid        b = potassium acetate/18crown-6                                               c = tetrabutylammonium acetate (no attempt was made to dry the catalyst       after purchase (Aldrich)                                                      d = tetrabutylphosphonium acetate (hygroscopic oil which was believed to      be wet)                                                                       *molar basis                                                                  **calculated from monomer to initiator ratio                             

Except in the noted cases, all reactions were run in bulk (90-160 gscale) under dry nitrogen, with mechanical stirring and with theexotherm controlled at 29°-33° C. through the use of a temperatureactuated 0° C. cooling bath.

The proceeding examples demonstrate that atactic or isotacticpoly(3-hydroxybutyrate) can be readily prepared with molecular weightsup to 150,000 (peak molecular weight) from the ring openingpolymerization of β-butyrolactone. Typically, reaction times are shownto be significantly less than one day (24 hours). The preceding examplesadditionally demonstrate the extreme water sensitivity for the anionicring opening polymerization of β-butyrolactone. High molecular weightpolymer and/or reasonable reaction rates of under one day were onlyobtained in the relative absence of water. Also demonstrated is the easewith which either linear or branched or star shaped polymers can beprepared based upon the choice of initiator used in the polymerizationof β-butyrolactone. These examples additionally teach the removal ofmonomer by precipitation of the polymer into water and/or thedecomposition of monomer in aqueous acetic acid.

The following four examples illustrate the preparation of blends ofpoly(3-hydroxybutyrate) and cellulose esters.

In addition to the novel precipitative blends described in Example17-19, physical mixing of the components to form a blend can beaccomplished in a number of ways such as mixing the components in theappropriate solvent (e.g., acetone, THF, CH2Cl₂ /MeOH, CHCl₃, dioxane,DMF, DMSO, AcOH, AcOMe, AcOEt, pyridine) followed by film casting orfiber extrusion. The blend components can also be mixed by thermallycompounding. The most preferred method is by thermally compounding in anapparatus such as a torque rheometer, a single screw extruder, or a twinscrew extruder. The blends produced by thermally compounding can beconverted to thin films by a number of methods known to those skilled inthe art. For example, thin films can be formed by discoating asdescribed in U.S. Pat. No. 4,372,311, by compression molding asdescribed in U.S. Pat. No. 4,427,614, by melt extrusion as described inU.S. Pat. No. 4,880,592, by melt blowing, or by other similar methods.The blends can be converted to molded plastic objects by injectionmolding as well as by extrusion into sheet from which an object is cutor stamped. The thermally compounded blends can be used for meltextrusion of fiber as well.

EXAMPLE 17

A solution of 42.09 grams of cellulose acetate propionate (DS(OPr)=2.65and DS(OAc)=0.1) dissolved in 250 milliters of methylene chloride wascombined with a solution of 28.46 grams of atacticpoly(3-hydroxybutyrate) prepared according to the present invention,(Mw=32,000, Mn=23,000) in 100 ml of methylene chloride. The resultingclear solution was precipitated into warm water (80° C.) and filtered.The white precipitate was washed well with hot water and dried in vacuoat 60° C. Differential Scanning Calorimetry (DSC) analysis of theprecipitated flake shows a single strong glass transition temperature Tgat 77° C. and a melting temperature (Tm) at 161° C. The dry precipitatewas transferred to a torque rheometer heated at 180° C. and thermallyblended for 5 minutes at 40 rpm blade speed. This blend was ground to 5mm particle size and pressed between two metal plates at 180° C.Physical properties of the films were as follows:

Tangent Modules 0.57×10⁵ psi

Break at Elongation 53%

Tensile Strength 3.06×10⁵ psi

Tear Strength 17.0 g/m1

Gell permeation chromatography (GPC) in THF shows two peaks; one with aweight average molecular weight Mw=228,000 and another of Mw=39,000.

EXAMPLE 18

A solution of 8.0 grams of cellulose acetate propionate (DS(OPr)=2.65and DS(OAc)=0.1) in 150 mls of propionic acid was combined with asolution of 2.0 grams of atactic poly(hydroxbutyrate) prepared accordingto the present invention in 50 mls of acetic acid to form a clearsolution. The solvent blend was then precipitated into 2 liters of coldwater. The resulting white precipitate was filtered and washed well withhot water. Analysis of the precipitate by DSC shows a single strong Tgat approximately 94° C. and a Tm at 165° C.

EXAMPLE 19

A solution of 40.12 grams of cellulose acetate propionate (degree ofsubstitution propionyl is 2.65 and acetyl is 0.10) dissolved in 300 mlsof propionic acid was combined with a solution of 41.5 grams of atacticpoly(hydroxybutyric acid) prepared according to the presentation(Mw=3.1×10⁵) dissolved in 200 mls of propionic acid at room temperature.The resulting clear solution was precipitated into 10 liters of waterand flake precipitated. The precipitate was washed well with water anddried under vacuum at 80° C. Differential scanning calorimetry show asingle strong Tg at 57° C. and a Tm at 155° C.

With the exception of the novel precipitative blending described hereinand above, blends and films are prepared by two general methods: (i) theblend components are shaken together before compounding at theappropriate temperature in a Rheometrics Mechanical Spectrometer. Theresulting resin is typically ground to 5 mm particle size and a portionis pressed between two metal plates at a temperature above the melttemperature of the resin (typically at 180° C.) to form a melt pressedfilm; (ii) blends of the cellulose ester and polyhydroxybutyrate wereprepared by dissolving the blend components, premixed at the desiredlevels, in 9/1 (v/v) CHC13/MeOH to give a 20% (w/v) solution. Films wereprepared by pulling down a portion of the solution on a glass plateusing a 15 to 30 mm draw blade. The films were allowed to air dryovernight before drying to a constant weight, in a vacuum oven at 40° C.

The tensile strength, break to elongation, and tangent modulus of thefilms are measured by ASTM method D882; the tear force is measured byASTM method D1938; the water vapor transmission rates are measured byASTM method F372. Inherent viscosities are measured at a temperature of25° C. for a 0.5 gram sample in 100 ml of a 60/40 by weight solution ofphenol/tetrachloroethane. Dynamic mechanical thermal analysis (DMTA)spectra were collected using a Polymer Laboratories Mk II at 4° C./minand 1 Hz.

EXAMPLE 20

The cellulose acetate propionate (CAP 482-20) used in the example is acommercial product sold by Eastman Chemical Company.

In a 300 ml round bottom flask, 16.0 grams of poly(hydroxybutyric acid)prepared as in Example 1 and 24.0 grams of cellulose acetate propionateCAP 482-20, degree of substitution propionyl is 2.7, and acetyl is 0.1)were dissolved in 160 mls of 9/1 chloroform/methanol at roomtemperature. The resulting clear solution was cast onto glass plates andthe solvent allowed to slowly evaporate. This film was used in thecomposting study which is summarized in Table 5.

Composting Studies--The following example provides a description ofgeneral procedures used in composting.

EXAMPLE 21

Composting can be defined as the accelerated natural degradative processthat results from putting organic matter in piles or heads to conservemetabolic heat; it entails the biologically mediated aerobicdecomposition of organic material to form CO₂, H₂ O, biomass, heat, andhumus.

Composting recipe:

The recipe for the synthetic waste that was used in the bench-scalecompost units consisted of purina rabbit chow (4,000 g), cow manure(1,000 g) garden soil (1,700 g), finely shredded newspapers (2,667 g),calcium carbonate (300 g), sodium bicarbonate (20 g) and water (10liters). Ingredients were mixed by a Hobart mixer until a uniformparticle size (1-3 mm) was obtained. The final mixture had a 55%moisture content and a pH of 6.8. Each compost cylinder receivedapproximately 7500 grams of the synthetic waste formula, which filledthe container completely. The film samples (1×16 cm) were uniformlydispersed throughout the mixture.

Compost Unit Design & Control System:

Bench-scale compost units were constructed from 11" diameter stainlesssteel piping. The cylinders were 17" in height,--with approximately 2"of headspace at the top and bottom. A fine mesh stainless steel screenwas inserted at the interface between the compost and the headspace tofacilitate air diffusion. In addition, the screens also prevented thecompost from obstructing the air inlet and outlet ports. The units weresealed with gas tight lids, permitting total gas collection via the ventport. The internal surfaces of the compost unit were fitted with 4baffles (13"×1") which enhanced the efficiency of mixing. Each cylinderhad a thermocouple probe inserted in the bottom third; this wasconnected to a Yokogawa temperature monitor which recorded thecontinuous temperature output of eleven individual compost units. Forcedair entered the unit through the primary inlet port, located at thebottom of the cylinder, and was shunted into the headspace. During theentire 15 day composting cycle, the primary air supply was fedcontinuously, delivering approximately 2,000 mls/min. When the metabolicheat caused the compost temperature to reach 55° C., it actuated a relayin the Yokogawa monitor. The relay in turn controlled a solenoid valvewhich permitted an additional 3,000 mls/min of air flow into thesecondary air inlet. All eleven compost units were controlledindependently. When the temperature fell below 50° C., the secondary airsupply was immediately shut off. Due to the high air flows which wererequired during the thermophilic phase, it was necessary to have boththe primary and secondary air streams flow through a water trap (tohumidify the air) prior to its entry into the cylinder.

Percent Moisture Determinations:

Samples of compost were taken daily and added to pre-tared pans; thesewere dried at 105° C. until a constant weight was obtained. The averagesample, approximately 10 grams, required at least 14 hours for drying.The percent water, and a dry weight correction factor were calculateddaily.

Compost Dry Weight Loss Determinations:

At the beginning of each experiment, a tare weight was determined foreach individual compost unit. During an experiment, each compost unitwas Weighed daily on a Metler PM 3000 top loading balance. The totalweight minus the tare weight being equal to the amount of compost on awet weight basis. To insure accuracy, all samples which were removed formoisture analysis or pH were weighed; these values were added back tothe previous day's total weight. The percentage dry weight multiplied bythe net wet weight yielded total dry weight.

Film Weights:

Film samples were dried in a vacuum oven held at 30° C. (under a lowstream of dry N2) until a constant weight was obtained. Due to the lowtemperature limits imposed by certain films, a desiccant was added tofacilitate drying. Many of the films possessed hygroscopic componentswhich retained water, consequently 3 to 4 days of drying were requiredbefore a constant weight could be obtained.

Compost pH:

Approximately 25 grams of compost were collected daily for pHdeterminations. To each sample, 40-50 mls of distilled water were added.Samples were allowed to sit for 30 minutes with periodic stirring tofacilitate mixing. After 30 minutes, the entire contents of thecontainer were poured through 4 layers of cheese cloth to remove alllarge particles. The precaution of filtering was necessary to insurethat no interference with the pH probe occurred. The pH of the extractwas then taken with an Orion model 611 pH meter.

Film washing:

Following the 15 day compost cycle, films were washed for 30 minutes. ina neutral detergent solution held at 50° C. for one hour. The detergentwas removed by extensive (4-6) distilled water rinses. Films were airdried, and then placed in a vacuum oven as described above.

Carbon, and Nitrogen Determinations:

Percent C, H, and N were determined on finely ground compost.

Statistical Design:

A maximum of eleven different types of films could be evaluated during asingle compost trial, with each compost unit receiving only one of theeleven test types. Each individual compost cylinder received thefollowing: 15 replicate test films, 10 replicate starch containingblends (Matter-Bi™ Navamont, Int'l (internal positive control), and 5replicate Polyethylene films (negative control). Following the 15 daycompost cycle, all films were harvested and processed in the mannerpreviously described. Following the washing and drying steps, a netpercent weight change was calculated for each individual film sample.

All internal control films (starch containing polymer Matter-Bi™) werefirst segregated by individual compost units and statistically analyzedto insure that no unit to unit bias existed. This was accomplished by ananalysis of variance using the General Linear Method (GLM) of SAS, inconjunction with a Duncan's Multiple Range Test of the individualcompost unit means at the 95% confidence level. The GLM model wasPERCENT=UNIT, where PERCENT=the percent weight loss of the starchcontaining polymer films (internal controls) after 15 days, and UNIT=theindividual compost cylinder. If this analysis revealed that there was nostatistical difference between units, with regard to the degradation ofthe internal positive control, it was then statistically valid tofurther analyze and compare the test films across different compostunits. All test films were sorted by film type prior to conducting theGLM analysis of variance. The model used was PERCENT=FILM, wherePERCENT--the percent weight loss of each film type after 15 days, andFILM=either starch containing polymer, polyethylene, orcellulose-acetate-propionate/poly-β-hydroxybutyrate.

RESULTS AND DISCUSSION

Bench-scale compost units were designed to emulate a municipal windrowcomposting operation, equipped with forced aeration for temperatureregulation. A comparison of moisture content, temperature profiles, pHchanges, and compost dry weight loss over 15 days, demonstrated that thebench-scale units were functioning in a manner analogous to theirfull-scale municipal counterparts. At the start of the experiment themoisture content was adjusted to 60%, it dropped slightly during thethermophilic phase which required higher air flows which had a tendencyto dry the compost. After five days the system started to actuallyproduce water, a by product of metabolism. The smaller unitsdemonstrated excellent self heating ability, with temperatures of55°-65° C. being reached within 2-3 days. Unfortunately, the microbialecosystem within a compost pile has an inherent tendency to self-limititself by the excessive accumulation of metabolically generated heat.The threshold for significant inhibition is approximately 60° C., andinhibition sharply rises at higher temperatures. Unless controlledthrough deliberate heat removal, composting masses typically peak at 80°C., at which point the rate of decomposition is extremely low. Highvolume solid waste management systems can not afford to have thedegradation process operate at low efficiencies, due to the relativelyshort time frame they are operating within. Thus, this self-limitingtendency must be aggressively countered if microbial decomposition is tobe encouraged. Consequently, the central problem in the design andcontrol of municipal composing facilities is heat removal, with anoperational ceiling held near 60° C. Forced aeration has been shown tobe a very effective means of removing heat. Since approximately ninetimes more air is required to remove heat than to supply the metabolicO₂ for aerobic respiration, these systems do not suffer from oxygenlimitations. The desired operational temperature ceiling for the benchscale units used in this study was between 55°-60° C. The control systemmaintained adequate control against deleterious temperatures.

Municipal systems have to handle, process, and reduce large volumes ofwaste in a short time frame so that they can meet new incoming loads.The bench scale compost units were able to cause a 42% loss in dryweight of the starting synthetic waste mixture--denoting excellentdegradative efficiency. The carbon to nitrogen (C:N) ratios of thestarting waste were typically lower for the bench-scale units than wouldbe experienced in most municipal waste streams. Compost used in thebench-scale units started with C:N ratios in the range of 25:1, whereasmost municipalities deal with waste streams that have C:N in excess of30:1.

The compost also under went macroscopic changes during the 15 days. Thefinal product was much darker than the starting material, and it had anodor which was very characteristic of fresh soil. These changes are alsoconsistent with the final product that municipal compost units produce.

Since each compost cylinder represents a single experiment and eachtrial represents eleven experiments, there was an important need todocument the efficiency of each unit with reference to an internalstandard. If unit-to-unit variation exists, conclusions made regardingdifferences between test films would not be valid. This obstacle wasovercome by the use of starch containing polymer films as an internalcontrol for each compost cylinder. If these control films degraded tothe same extent in all eleven compost units, then it was statisticallyvalid to compare and contrast the different test films across or betweenunits. Use of control films also permits a historical comparison offilms evaluated in separate composting trials.

EXAMPLE 22

Three films; starch containing polymer (Matter-Bi™), polyethylene films,and the experimental polymer blend produced in Example 20 (40 wt %synthetic, atactic poly(3-hydroxybutyrate) and 60 wt % CAP 482-20) weresubmitted to the composting conditions described in Example 21.

The mean percent weight loss for cellulose-acetatepropionate/poly-p-hydroxybutyrate, starch containing polymer, andpolyethylene films are summarized in Table 5. All three film types arestatistically different from one another at the 90% confidence level.Although the starch containing polymer films yielded the most weightloss, the rigid starch component of these films degraded preferentially,leaving behind a very flexible polymer. These composting studiesindicate that these films will not pass through the final screens atmost municipal compost facilities. The celluloseacetate-propionate/poly-βhydroxybutyrate films lost an average of 24% oftheir original weight. These films were noticeably less flexible andwere easily torn. The polyethylene films were completely recalcitrant toall microbial degradation--these films actually gained a small amount ofweight which probably represents organic matter that had adsorbed to thefilms surface.

                  TABLE 5                                                         ______________________________________                                        Film Weight Loss After 15 Days in Bench Scale Compost                         Units                                                                                         Sample     Percent Weight                                     Film Type       Replications                                                                             Loss                                               ______________________________________                                        Starch Containing Blend                                                                       115        52.0 ± 2.4                                      Experimental Blends:                                                                          15         24.5 ± 9.5                                      CAP 482-20/Poly                                                               (3-Hydroxybutyrate                                                            (60/40)                                                                       Polyethylene    15         -0.9 ± 1.2                                      ______________________________________                                    

To further substantiate that the weight loss for the blend of PHB/CAP482-20 (40/60) was due to the PHB component, a series of 14 compostedfilms and 3 pre-composting films were analyzed by proton NMR (CDCl₃).The results of this NMR analysis are presented in Table 6. The relativeamount of CAP 482-20 was calculated from the area contribution ofcarbohydrate CH and CH2 protons. The degree of substitution could thenbe calculated from the propionyl region (methyl) of the NMR. Based onNMR and hydrolysis methods the DS of acetate in CAP 482-20 waspreviously known to the approximately 0.1. The relative amount of PHBwas conveniently calculated from the area contribution of the PHB methylgroup.

                  TABLE 6                                                         ______________________________________                                        Ratio of PHB to CAP 482-20 in a 40/60 Blend Before and                        After Composting                                                                          NMR Determined                                                                Total DS* for                                                                              Percent PHB                                          Sample      CAP Component                                                                              in Blend (NMR)                                       ______________________________________                                        Before      2.85 +/- 0.006**                                                                           42.2 +/- 0.23                                        Composting                                                                    After       2.87 +/- 0.068                                                                             29.12 +/- 7.5                                        ______________________________________                                         *The DS of propionyl was determined directly from the NMR integral. It wa     then assumed that the acetyl DS was 0.1. Thus, total DS = propionyl DS +      0.1.                                                                          **Error is expressed as one standard deviation.                          

EXAMPLE 23

This example, though the use of a radiolable study, demonstrates thatCAP 482-20 (used in the experimental blend of Table 5) does not undergosignificant degradation (composting) in the absence of atacticpoly(3-hydroxybutyrate).

Radiochemistry:

Activated sludge from the Tennessee Eastman Chemical Company'swastewater treatment system served as the starting inoculum for theestablishment of the stable CA degrading enrichment cultures used inthis invention. Cellulose ester degrading enrichments were initiated ina basal salts medium containing the following ingredients per liter: 50ml of Pfenning's macro-mineral solution, 1.0 ml of Pfennig's traceelement solution, 0.1% (wt/vol) Difco yeast extract, 2 mM Na₂ SO₄, 10 mMNH₄ Cl which supplements the ammonia levels provided by Pfennig'sMacro-mineral solution, 0.05% (wt/vol) cellobiose, 0.05% (wt/vol) sodiumacetate. This solution was adjusted to pH 7.0 and a final volume of 945ml before being autoclaved at 121° C. at 15 psi for 15 minutes. Aftercooling to room temperature, 50 ml of sterile 1 M phosphate buffer and 5ml of a complex vitamin solution which has been filtered through a 0.2μm filter were added. The test cellulosic film was then added, and theflask was inoculated (5% v/v) with activated sludge (biomass) from thewastewater treatment system. The flask was placed on a New Brunswickshaker (Model 2300 Innova) situated in a walk in incubator held at 30°C. and 250 rpm. A stable microbial population was thus obtained byserially transferring the culture every 3 weeks. This basal salts mediawas used in all the in vitro film degradation experiments. Two examplesof ₁₄ C cellulose acetate propionate (total DS=2.64 and 2.44) wereprepared with ₁₄ C propionyl chloride labeled in the carboxyl carbon.These labeled samples were then incubated separately in the in vitroenrichment cultures for approximately 650 hours at 30° C. This systemwas chosen over a compost environment because of its higher degradativeactivity against cellulose esters.

Both samples showed less than 1% of the theoretical amount ofradioactivity released as carbon dioxide in 644 hours. This demonstratesthat only minor weight loss could have been expected from the CAP 482-20(DS=2.8) component which was used in the blend with atacticpoly(3-hydroxybutyrate, PHB) (Table 5).

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:
 1. A process for producing poly(3-hydroxy-alkanoates)comprising contacting a solution containing about 1 to about 100 molepercent of at least one β-substituted-β-propiolactone containing lessthan 2,790 ppm water with an anionic initiator under polymerizationconditions to produce a poly(3-hydroxyalkanoate) wherein theβ-substituted-β-propiolactone is of the formula: ##STR18## ##STR19##wherein n is an integer from 10 to 12,000 and R and R¹ are eachindependently selected from the group consisting of C₁ to C₂₀ alkyls andsubstituted alkyls, C₃ to C₁₀ aryls and substituted aryls, and C₅ to C₁₀cycloalkyls and substituted cycloalkyls and wherein R¹ is also selectedfrom the group consisting of hydrogen.
 2. The process according to claim1 wherein the β-substituted-β-propiolactone contains less than 2,000 ppmwater.
 3. The process according to claim 1 wherein theβ-substituted-β-propiolactone is optically enriched wherein one of 2possible enantiomers is present in an enantiomeric excess of 30-100% andproduces at least partially isotactic poly(3-hydroxyalkanoate).
 4. Theprocess according to claim 1 wherein the contacting temperature isbetween 0° and 150° C.; the molar ratio of initiator toβ-substituted-β-propiolactone is between 1/25 and 1/12,000; and thepolymerization is conducted in 0 to 90 wt. % of an aprotic solvent. 5.The process according to claim 4 wherein the contacting temperature isbetween 25° and 60° C. and the molar ratio of catalyst to β-substitutedpropiolactone is between 1/200 and 1/8,000.
 6. The process according toclaim 1 wherein the polymerization is conducted for less than 24 hours,the conversion is greater than 60%, and n is greater than
 100. 7. Theprocess according to claim 1 wherein the poly(3-hydroxyalkanoate) isprepared by sequential treatment of the polymerization mixture withβ-substituted-β-propiolactones of differing structure or enantiomericcomposition thus producing a block copolymer.
 8. The process accordingto claim 1 wherein the carboxylic acid content in the β-substituted-βpropiolactone monomer is less than 0.5 mole %.
 9. The process accordingto claim 1 wherein the anionic initiator is an anionic carboxylate. 10.The process according to claim 9 wherein the cation of the anionicinitiator is selected from the group consisting of alkaline earthmetals, alkali metals, tetrasubstutited ammonium compounds,tetrasubstituted phosphonium compounds, tetrasubstituted arseniccompounds tetrasubstituted antimonium compound, tetrasubstitutedbismuthium compounds, trisubstituted sulfonium compounds, and transitionmetal cations in oxidation states of 5 or less and the anion is suchthat the pK_(a) of the conjugate acid of the anion is at or above 1.5.11. The process according to claim 10 wherein the alkali metals areselected from the group consisting of rubidium and cesium.
 12. Theprocess according to claim 1 wherein the pKa of the conjugate acid ofthe anion is at or above 4.0.
 13. The process according to claim 10wherein the anionic catalyst contains a chelating agent capable ofcomplexing to the cation of the anionic initiator.
 14. The processaccording to claim 10 wherein the process is conducted in the presenceof a catalyst/initiator in a mole ratio of 0.01 to 0.0001 relative tomonomer.
 15. The process according to claim 13 wherein the chelatingagent is selected from polyethers that are present in a concentration ofat least 1 mole equivalent relative to the cation of the anionicinitiator.
 16. The process according to claim 15 wherein the polyethersare selected from the crown ethers and cryptands.
 17. The processaccording to claim 10 wherein the anionic initiator is selected frompotassium carboxylates or cesium carboxylates in the presence of18-crown-6 chelating agent.
 18. The process according to claim 10wherein the anionic initiator is cesium acetate.
 19. The processaccording to claim 10 wherein the cation of the anionic initiator isselected from fully substituted ammonium or phosphonium cations.
 20. Theprocess according to claim 19 wherein the anionic initiator istetrabutylammonium acetate.
 21. The process according to claim 1 whereinthe β-substituted-β-propiolactone is distilled at a temperature below100° C. and under conditions sufficiently mild such that decompositionof β-substituted-β-hydroxypropionate to produce water does not occur.22. The process according to claim 1 wherein theβ-substituted-β-propiolactone is distilled prior to use inpolymerization such that the low boilers are continuously removed. 23.The process according to claim 1 further comprising precipitating thepoly(3-hydroxyalkanoate) to remove unreacted monomer into thesupernatant liquid.
 24. The process according to claim 23 wherein thepoly(3-hydroxyalkanoate) is poly(3-hydroxybutyrate) of atacticstereorandom composition and is dissolved in acetic acid containing upto 60% water and purified by precipitation into water.
 25. The processaccording to claim 1 wherein unreacted monomer is chemically decomposedin the presence of polymer by the addition of a nucleophile capable ofpreferentially reacting with monomers.
 26. The process according toclaim 1 wherein unreacted monomer is chemically decomposed in thepresence of polymer by the addition to the polymer of a polar solventselected from the group consisting of water and alcohol.
 27. The processaccording to claim 26 wherein the unreacted monomer is chemicallydecomposed at a temperature between 25° and 200° C.
 28. A processaccording to claim 26 wherein the unreacted monomer is chemicallydecomposed in the presence of an acid or base catalyst.
 29. The processaccording to claim 26 wherein the unreacted monomer is chemicallydecomposed in the presence of cosolvent that solublizes both the polymerand the polar solvent.
 30. The process according to claim 24 furthercomprising heating an aqueous acetic acid solution of thepoly(3-hydroxybutyrate) prior to the last precipitation at a temperaturebetween 60° and 140° C. for at least 1 minute to remove monomer bydecomposition.
 31. The process according to claim 24 wherein thepoly(3-hydroxybutyrate) is precipitatively blended with one or moreadditional polymers in which all polymers are precipitated fromsolution.
 32. The process according to claim 21 wherein theprecipitative blend is with a cellulose ester of DS 1.7 to 2.8.